Arts, Faculty of
Classical, Near Eastern and Religious Studies, Department of
DSpace
UBCV
Steinhoff, John Paul
Master of Arts - MA
University of British Columbia
This thesis reviews the research and theoretical models of Alan Richardson on Roman camps and forts in Britain and applies the models to Roman forts located in North Africa. Richardson developed his models from ancient textual sources, a thorough examination of Roman camps and forts throughout Britain, and intuitive mathematical reasoning. For this paper, the most important model produced by Richardson during his study was a model which utilizes the perimeter dimensions of a fort to predict the type of military unit that the fort was designed to house, as each Roman military unit had varying space requirements. This is significant to the study of the Roman military in North Africa because often little archaeological evidence from Roman forts remains other than perimeter dimensions. This is a powerful tool to examine and enhance our understanding of the epigraphic evidence available, as this model has been extremely accurate predicting the type of military unit when compared to inscriptional evidence. The successful application of Richardson’s models in two separate frontier regions suggests that this was indeed how the Roman military went about constructing camps and forts throughout the empire during the 2nd century AD. Furthermore, the fort model is used to explore troop distribution in the frontier regions of Britain and Numidia during the reign of Hadrian. The results suggest that these two areas associated with linear barriers, Hadrian’s Wall in Britain and the African Fossatum in Numidia, were manned by a similar number of troops and were managed as their own distinct military entity.
THEORETICAL APPROACHES TO ROMAN CAMP AND FORT DESIGN: AN EXAMINATION OF THE FRONTIERS IN BRITAIN AND NORTH AFRICA UNDER HADRIAN by JOHN PAUL STEINHOFF B.Sc., Northern Michigan University, 2012 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Ancient Culture, Religion & Ethnicity) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2019 © John Paul Steinhoff, 2019 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled: Theoretical Approaches to Roman Camp and Fort Design: An Examination of the Frontiers in Britain and North Africa under Hadrian submitted by John Paul Steinhoff in partial fulfillment of the requirements for the degree of Master of Arts in Ancient Culture, Religion & Ethnicity Examining Committee: Dr. Leanne Bablitz Supervisor Dr. Robert Cousland Supervisory Committee Member Dr. Hector Williams Supervisory Committee Member iii Abstract This thesis reviews the research and theoretical models of Alan Richardson on Roman camps and forts in Britain and applies the models to Roman forts located in North Africa. Richardson developed his models from ancient textual sources, a thorough examination of Roman camps and forts throughout Britain, and intuitive mathematical reasoning. For this paper, the most important model produced by Richardson during his study was a model which utilizes the perimeter dimensions of a fort to predict the type of military unit that the fort was designed to house, as each Roman military unit had varying space requirements. This is significant to the study of the Roman military in North Africa because often little archaeological evidence from Roman forts remains other than perimeter dimensions. This is a powerful tool to examine and enhance our understanding of the epigraphic evidence available, as this model has been extremely accurate predicting the type of military unit when compared to inscriptional evidence. The successful application of Richardson’s models in two separate frontier regions suggests that this was indeed how the Roman military went about constructing camps and forts throughout the empire during the 2nd century AD. Furthermore, the fort model is used to explore troop distribution in the frontier regions of Britain and Numidia during the reign of Hadrian. The results suggest that these two areas associated with linear barriers, Hadrian’s Wall in Britain and the African Fossatum in Numidia, were manned by a similar number of troops and were managed as their own distinct military entity. iv Lay Summary Our understanding of the Roman military has been enhanced by varying types of evidence such as archaeological, inscriptional, and textual. This study aims to increase our understanding of the Roman military by examining the topic of how they designed camps and forts. While using existing types of evidence, this thesis mainly utilizes theoretical models developed from the study of Roman camps and forts in Britain to examine Roman forts located in North Africa with a particular focus on the Roman province of Numidia (modern day Algeria) under the reign of emperor Hadrian during the 2nd century AD. Through these models, a better understanding of the existing evidence is achieved. Additionally, topics like troop distribution and cavalry-to-infantry ratios can be assessed more accurately. v Preface This dissertation is original, unpublished, independent work by the author, John Paul Steinhoff. vi Table of Contents Abstract…………………………………………………………………………………………...iii Lay Summary…………………………………………………………………………………......iv Preface……………………………………………………………………………………………..v Table of Contents…………………………………………………………………………………vi List of Tables …………………………………………………………………………………..viii List of Figures…………………………………………………………………………………......x Acknowledgements……………………………………………………………………………….xi Dedication………………………………………………………………………………………..xii Chapter 1: Introduction …………………….………......................................................................1 1.1 Introduction and Summary ...…………………………………………………………1 1.2 Previous Attempts to Classify Military Units with Camps and Forts…………………2 1.3 Benefits of this Study………………………………………………………………….4 1.4 Proposal………………………………………………………………………………..7 Chapter 2: Origins of the Roman Camp…………………………………………………………..9 2.1 Early Stages…………………………………………………………………………...9 2.2 The Roman Camp Plan................................................................................................10 2.3 The Republican Camp of Polybius…………………………………………………..14 2.4 Larger Camps…………………………………………………………….…………..16 2.5 Calculating Camp Dimensions………………………………………………………17 2.6 The Evolution of the Camp Paradigm……………………………………………….18 2.7 Influence of Land Surveying Technology…………………………………………...19 Chapter 3: The Camp of the Imperial Army ……………………………………………………22 3.1 Organization of Imperial Army……………………………………………………...22 3.2 De Munitionibus Castrorum…………………………………………………………23 3.3 Aspect Ratio……………………………………………………….…………………24 3.4 Calculating Dimensions of an Oblong Camp……………………………….……….26 3.5 Notional Cohorts…………………………………………………………………….28 3.6 The Multiplier in the Hyginian Camp……………………………………….………31 3.7 The Intervallum of Imperial Camps…………………………………………………33 3.8 Acreage of Imperial Army Camps…………………………………………………..33 3.9 Partition of Space and Summary of Imperial Camp Model…………………………34 Chapter 4: Forts, Fortlets, and Legionary Fortresses ……………………………………………36 4.1 Fort Measurements…………………………………………………………………...36 4.2 Aspect Ratio of Forts………………………………………………………………...37 vii 4.3 The Intervallum Width of Forts………………………………………………….….38 4.4 The Fort Model……………………………………………………………………...39 4.5 Classifying Forts According to Unit………………………………………………...41 4.6 Fortlets…………………………………………………………………………….…42 4.7 Legionary Fortresses…………………………………………………………………44 4.8 Manpower and Defense of Forts, Fortlets, and Legionary Fortresses………………46 Chapter 5: The British and North African Frontier Forts under Hadrian ……………………49 5.1 Hadrian’s Wall……………………………………………………………………….49 5.2 Hadrian’s Wall Fortlets………………………………………………………………51 5.3 The African Fossatum……………………………………………………………….52 5.4 The Forts of the African Fossatum under Hadrian………………………………….57 5.5 Summary of Numidian Forts with Recorded Dimensions…………………………..58 Chapter 6: The British and Numidian Frontier Garrisons under Hadrian ……………………63 6.1 The British Frontier Garrison………………………………………………………...63 6.2 The Numidian Garrison……………………………………………………………...64 Chapter 7: Best-Fit Mixed Unit Model……..……………………………………………………67 7.1 Logic behind Model………………………………………………………………….67 7.2 Best-Fit Results………………………………………………………………………70 Chapter 8: Conclusions ……………………………………………………………………72 Bibliography……………………………………………………………………………………..74 viii List of Tables Table 1.1: Partition of Space within Camps ……………………………………………………..4 Table 2.1: Camp Models for a Century ……………………………………………………13 Table 2.2: Space Allocations in the Polybian Camp ……………………………………………15 Table 2.3: Geometric Properties of a Square ……………………………………………………16 Table 2.4: Camp Area and Perimeter in Relation to the Number of Infantry ……………17 Table 3.1: Composition of Units in the Imperial Army ……………………………………22 Table 3.2: Frequency of Aspect Ratio of Roman Camps ……………………………………25 Table 3.3: Space Allowances in Camps Derived from Hyginus ……………………………29 Table 3.4: Troop Numbers and Space Uptake in the Hyginian Camp ……………………32 Table 3.5: Base Rectangle Areas and Intervallum Widths of the Masada Camps ……………33 Table 3.6: Relationship of Cohort Equivalents to Base Rectangle and Area over the Rampart…34 Table 4.1: North African Fort Measurements in Actus ……………………………………36 Table 4.2: Frequency of Aspect Ratio of North African Forts ……………………………37 Table 4.3: Intervallum Width as a Fraction of the Area it defines in Some Roman Forts ……39 Table 4.4: Notional Cohort Values of Units of the Roman Army ……………………………40 Table 4.5: Units Housed by Fort Groups ……………………………………………………42 Table 4.6: North African Forts by Group ……………………………………………………43 Table 4.7: Numbers of Men in British and Numidian Fortlets ……………………………44 Table 4.8: Legionary Fortresses ……………………………………………………………45 Table 4.9: Intervallum Width as a Fraction of the Area it defines in Legionary Fortresses ……46 Table 4.10: Men Needed to Man the Ramparts of Forts, Fortlets, and Fortresses ……………47 Table 5.1: Notional Cohort Signatures of Hadrian’s Wall Forts ……………………………51 ix Table 5.2: Hadrian’s Wall Fortlets ……………………………………………………………52 Table 5.3: Numidian Forts under Hadrian ……………………………………………………58 Table 6.1: The Garrison of the British Hadrianic Frontier ……………………………………64 Table 6.2: The Garrison of the Numidian Hadrianic Frontier ……………………………65 Table 7.1: Summary of Best-Fits for Equitata Forts along Hadrianic Frontiers ……………70 x List of Figures Figure 2.1: Roman Camp Plan ……………………………………………………………11 Figure 2.2: Inter-relationship between Vallum and Tented Area ……………………………12 Figure 2.3: The Polybian Camp ……………………………………………………………15 Figure 2.4: Reconstruction of a Groma ……………………………………………………20 Figure 3.1: Sub-squares in Rectangles with n:(n+1) Aspect Ratio ……………………………27 Figure 4.1: Comparative Plans of 2nd and 3rd Century Forts ……………………………………38 Figure 5.1: Map of Hadrian’s Wall………………………………………………………………50 Figure 5.2: The Numidian Limes under Hadrian………………………………………………...53 Figure 5.3: Features of the Fossatum ……………………………………………………………54 Figure 5.4: Linear Barriers and Transhumant Routes in the Frontier-zone ……………………56 xi Acknowledgements I would like to thank my supervisory committee for their enduring patience and guidance throughout the process of writing my thesis. I would also like to thank my mother, sister, and brother-in-law for their support over these past few years while pursuing my degree. xii Dedication To My Father I hope you are proud 1 Chapter 1: Introduction 1.1 Introduction and Summary This dissertation utilizes theoretical models developed by Alan Richardson from his study of Roman camps and forts in Britain, mostly dating to the 2nd century AD, to investigate contemporary Roman forts in North Africa. Richardson’s series of published papers from 1997 through 2003 culminated in a British Archaeological Report (BAR) series publication in 2004 titled Theoretical Aspects of Roman Camp and Fort Design. His models, along with historical sources from Polybius and Hyginus, were developed from the standard features of vallum (rampart) and ditch, intervallum (open space), and inner area displayed by all Roman camps and forts with rounded corners, also known as playing-card shaped forts, from the end of the 1st century AD to the beginning of the 3rd century AD. The most significant model developed by Richardson for the study of playing-card shaped forts in North Africa utilizes perimeter dimensions to predict the type of military unit for which the fort was designed since little archaeological evidence often remains of Roman forts in North Africa other than perimeter dimensions. During the aerial surveys of the African Fossatum in the late 1940’s under the direction of Colonel Jean Baradez, and in his subsequent publications, the outlines and measurements of many Roman forts were recorded. Additionally, in her 1979 publication The Roman Army in Numidia Elizabeth Fentress summarized much of the pertinent information from previous scholarship such as fort dimensions, position, and inscriptional evidence. These works provide the necessary information to test Richardson’s model on the Roman playing-card shaped forts of North Africa and verify its accuracy through a comparative analysis with the available 2 inscriptional evidence. While the sample is smaller, the results from the study of Roman playing-card shaped forts in North Africa indicate that Richardson’s model is accurate and applicable elsewhere. Therefore, implying that the paradigm for fort and camp construction was most likely utilized throughout empire from the late 1st to early 3rd century AD. 1.2 Previous Attempts to Classify Military Units with Camps and Forts There have been previous attempts to classify Roman forts and camps with a corresponding military unit or number of troops. A study by W.S. Hanson, also utilizing Hyginus, produced a rough estimate of 350 men per acre.1 All of these previous attempts to classify units by fort dimensions or other means fall short for various reasons. In the case of barracks and granaries, most forts do not have enough archaeological evidence remaining to utilize this type of approach: as Anne Johnson writes, “Unless a fort has been totally excavated we cannot be certain that the full complement of granaries has been discovered.”2 Over-the-ramparts measurements in acres, while accurate at times, add more variables to the equation in the form of varying ditch and rampart widths. Using fort dimensions at the inner edge of the rampart eliminates the additional variables associated with over-the-ramparts measurements, and does not have the same restrictions that accompany using barracks or granaries to determine the associated garrison, but still must address the varying dimensions of camps and forts constructed to house military units composed of an equivalent number of men. Some scholars argue that this theoretical approach does not produce significant results. Anne Johnson writes, “There are too many unknown factors involved to make this kind of 1 Hanson 1977, 142–143. 2 Johnson 1983, 293. 3 calculation meaningful.”3 Johnson, and later Terence Coello, uses the obvious argument that inscriptional evidence indicates that Roman forts of similar dimensions sometimes housed varying sized units, and similarly sized units may have been housed in forts with different dimensions.4 While Johnson’s claims seem insurmountable, she admits, “the fort builders clearly worked within the guidelines of a standard military manual, the forts were far from standardized in their internal details.”5 Richardson’s model, unlike previous classification attempts, reveals the underlying paradigm or guidelines by which military engineers worked, which demonstrates the amazing flexibility, not the perceived inconsistencies, of the Roman camp and fort system. My research on Roman forts in North Africa strengthens the arguments expounded by Richardson in his work on camps and forts in Britain. In his model Richardson addresses the concerns of H. Welfare that unusable ground at larger camps would make a simple formula problematic.6 Only a percentage (referred to as the multiplier) of the inner area was used to house soldiers, while the rest of the space was used for standard administrative functions and roads (Table 1.1). Richardson’s model reveals that over half of the space (52%) within the rampart (R) was not needed for men’s tents, and provided more than enough space to work around any patches of unsuitable ground. The intervallum, while mainly used to muster troops and defend against enemy fire, could be encroached upon slightly by stores, booty, prisoners, or tents when necessitated by unsuitable ground.7 Smaller camps had the luxury of avoiding unsuitable ground in the first place. 3 Johnson 1983, 293. 4 Coello 1996, 56. 5 Johnson 1983, 291. 6 Welfare and Royal Commission on Historical Monuments 1995, 10. 7 Richardson 2004, 32. 4 Table 1.1 Partition of space within camps (Richardson 2004) (R = area within the rampart; A = area within the intervallum) Area % R % A Within the intervallum (A) 64% Of the intervallum 36% Strigae (men’s tents) 48% 48 / 64 = 75% Praetorium, roads, etc. 16% 16 / 64 = 25% 1.3 The Benefits of This Study Beyond the concerns of validity for scholars such as Johnson or Welfare, one might ask what the results from a study of this nature can say about the Roman army. To start with, Richardson’s models do not indicate what was happening “on the ground” at a particular point in time. His models are used to calculate the types of units that a camp or fort could house, but not how many soldiers were actually there at a specific moment. In areas like North Africa where little material evidence has been uncovered besides fort perimeters, issues of hypothetical troop distribution can be assessed. An examination of troop distribution provides a glimpse into the thought processes and strategy of the Roman military machine. A comparison of the forts along the Hadrianic frontiers of Britain and North Africa suggests that both Hadrian’s Wall and the much longer African Fossatum, while quite different in construction, were manned by the same number of troops, equivalent to 30 notional cohorts. A notional cohort number (N) is a theoretical expression of space requirements needed for a cohort. A cohors quingenaria peditata, consisting of 480 infantry, becomes the base unit (N = 1) from which all other types of military units space requirements can be calculated. For example, a cohors milliaria peditata of 800 infantry (N = 1.67) is determined by dividing the amount of 5 infantry by 480 (800/480 = 1.67). This process, called a transformation in mathematics, would allow a Roman military engineer to calculate the space requirements of large numbers of troops. The appearance of several armies in the historical sources with a legion and its auxiliaries totaling 30 notional cohorts suggests that Hadrianic linear frontiers and barriers throughout the empire may have been managed as their own distinct military entities. Josephus describes a legion with its auxilliaries that produce a notional cohort number of 30.8 He later writes about a three legion army and its auxilliaries with a notional cohort number that totals 90.9 Additionally, Tacitus describes a two legion army with its auxilliaries totalling a notional cohort number of 60.10 Each of these examples provides literary evidence to support the hypothesis that frontier regions may have been considered and managed as their own distinct military unit, much like an army on campaign. Furthermore, an accurate picture of troop distribution can reveal areas with more densely concentrated numbers. This information indicates what areas may have been of the greatest concern to the Romans, perceived or real, in frontier regions. A study of this nature can also enhance our understanding of inscriptional and epigraphic evidence. Often, inscriptions from forts that indicate the presence of a certain military unit are fragmentary. Even when a full inscription is present, an auxiliary unit was sometimes not explicitly described as peditata or equitata. Also, it is usually not indicated whether it was quingenaria or milliaria. By calculating the notional cohort number, or unit’s signature associated with a fort, it becomes quite clear whether the auxiliary unit indicated on the inscription was peditata or equitata, and quingenaria or milliaria and allows for a more specific definition of that unit. Richardson notes that the model on its own should not necessarily over- 8 Josephus II.498, trans. Williamson. 9 Josephus III.71. 10 Tacitus Agricola XXXV, trans. Grant. 6 rule other opposing evidence, but that when the model conflicts with other evidence, a thorough re-examination of the existing evidence should be performed.11 A final obstacle that must be considered when addressing the relationship between troop numbers and fort dimensions is the phenomenon of changing unit type during the life of a single fort that does not experience changes to its perimeter defenses. Richardson’s research, coupled with my work on Roman forts in North Africa, indicates that Roman forts were intentionally designed to satisfy the space requirements of a small range of military units. Most forts could house two or three different size units at a space allowance of six to eight actus quadrati. An actus quadrati is the square of the actus, 120 Roman feet, making the actus quadrati 14,400 square Roman feet. While this will all be explained in detail in later chapters, a brief example may help to clarify. The fort at Wallsend on Hadrian’s Wall measures 8.6 actus quadrati within the intervallum. A cohors quingenaria peditata could fit into Wallsend at a space allowance of eight actus quadrati and a cohors quingenariae equitata at a space allowance of six actus quadrati. According to Breeze and Dobson, the fort at Wallsend housed an unknown cohors quingenariae equitata unit under Hadrian, the cohors II Nerviorum civium Romanorum under Marcus Aurelius, and the cohors IV Lingonum equitata in the third century.12 The example at Wallsend demonstrates how the Romans designed their forts with the capability to change the military unit stationed in order to have enough men for the perimeter defenses. Wallsend does not appear to have undergone changes to the design of its barracks either, whereas in the case of Strageath and Valkenburg, the perimeter defenses remained constant but the barracks were rebuilt to accommodate the new unit.13 Again, Richardson’s model reveals the guidelines that 11 Richardson 2004, 35. 12 Breeze and Dobson 2000, 256. 13 Davison 1989, 170–171. 7 these forts were constructed under, which intentionally allowed for a small range of units to be housed at a single fort within specific, preset space allowances. 1.4 Proposal The first section of this dissertation (Chapters Two and Three) examines the premise and work behind Richardson’s camp model. Chapter Two addresses theoretical issues concerning the origins of the Roman camp and the manpower required to construct field fortifications, as well as a discussion on troop spacing for the defense of camp perimeters. The three ancient authors utilized by Richardson to provide information about Roman camp layouts are Polybius, Josephus, and Hyginus. In The Jewish Wars, Josephus provides an account of how the Romans went about site clearance for camps, as well as the make-up of several historical armies. In Chapter Two, a detailed account of the Republican camp layout by Polybius, which supplies historical evidence for an early camp model, is discussed. Chapter Three examines the camp of the Imperial army through Richardson’s model derived from the De Munitionibus Castrorum by Hyginus, which was an attempt to create a manual for laying out a camp for an army of imperial date. The second section of this dissertation (Chapters Four through Seven) moves to the study of forts, the linear barriers associated with them, and the application of a revised formula to forts originally designed by Richardson for camps. Chapter Four explores some features of North African forts, as well as Richardson’s model for determining fort garrisons, which is an adaptation of the camp model, as forts are similarly defined, having rectangular perimeters, a vallum, intervallum, and an inner area for tents or barracks in the case of forts. I apply this model to the forts located on the British and Numidian frontiers in Chapter Five. Chapter Six compares 8 the distribution of troops along Hadrian’s Wall and the African Fossatum, while Chapter Seven explores the original and revised versions of the best-fit model for forts housing mixed equitata auxiliary units along both of these linear frontiers. This best-fit model, which will be explained in detail later, offers an avenue to examine differences in cavalry organization through infantry-to-cavalry ratios. My application of this model to the forts of North Africa with mixed equitata groups required a slight adjustment to Richardson’s formula due to the difference in space allowance for units in camps and forts. Results from this revised best-fit model suggest that the forts of equitata groups in Numidia were designed with slightly more generous space allowances than the equitata groups of Hadrian’s Wall. The smaller space allowances for equitata groups along Hadrian’s Wall may also coincide with the rush to finish constructing the wall itself. The combined application of Richardson’s theoretical models, developed from the forts and camps in Britain and applied to the forts in North Africa, offers valuable tools to augment our understanding of how the Roman military operated in these frontier provinces when scant material evidence remains. 9 Chapter 2: Origins of the Roman Camp 2.1 Early Stages The origins of Roman camp design are not fully known, but the Roman Republican army perfected the art of field fortifications, a technology that mainly involved the making of fortified camps, but could include any form of trenching and embanking for tactical purposes.14 Although field fortifications were used by the Greeks, they were irregular and conformed to the natural surroundings as much as possible. The Greeks, Polybius wrote, …think above all of the security they can achieve by exploiting the natural strength of the position, first because they grudge the labor involved in trenching, and secondly because they think man-made defenses are inferior to those provided by natural features of the site.15 On the other hand, it seems that the Romans had developed some standardized method of camp fortification by 300 BC. While there is no direct evidence of how the Romans approached the problem of field fortifications, the features of later Roman camps and forts give some clues to the original thinking. The basic premise of defending one’s ground from an elevated position behind an obstacle that impeded the enemy was not revolutionary, as many pre-historic settlements feature earthen banks and ditches, but the Romans applied a clear understanding of ergonomics, that is the quantitative aspects of the effort involved in making and defending them. The Romans seemed to have measured the amount of work an infantryman could perform without overexerting himself and used this information to inform the design of the camp and then fix the composition of the infantry units.16 14 Richardson 2004, 4. 15 Polybius VI.42, trans. Scott-Kilvert. 16 Richardson, 2003, 312; Richardson 2004, 4. 10 2.2 The Roman camp plan The Roman camp engineers had to balance the conflict between the shortest defensive perimeter (men-per-unit length of perimeter) and having enough room within the camp (men-per-unit area). The shortest perimeter for any given area is a circle, but would only allow for one fixed datum point from which to measure. The next convenient outline would be a square. This model chosen by the Romans had two central roads intersecting at right angles with tents being pitched along side streets running parallel to the main roads. The tented area would be confined by a rampart (vallum) and an outer ditch (fossa). An intervening space between the tented area and outer perimeter (intervallum) was allowed for organizing the defense (Fig. 2.1).17 Again, there is no direct evidence of a project to produce this design, but features of later Roman camps strongly suggest it. The task was to define a rule for calculating camp dimensions for the number of troops. The model was almost certainly designed to be performed with the smallest infantry unit, the century, with the intent of scaling up the model. The planner would first have to consider the spacing necessary for the perimeter defense using hand-held weapons without overcrowding or allowing gaps in the defense.18 For example, a century of 100 men, when placed within a square, would leave 25 men per side. If the spacing was six feet, that would make 150 feet per side. If the basic surveying unit of the actus of 120 Roman feet was used; that would leave 4.8 feet of perimeter per man to defend. The area enclosed would be one actus quadratus or 14,400 square feet. If the situation required equal spacing of the soldiers around the perimeter, a century of 80 men would have six feet of perimeter apiece to defend for an actus quadratus. 17 Richardson 2004, 5. 18 Richardson 2004, 5. 11 Figure 2.1 Roman Camp Plan (Richardson 2004) V = vallum I = intervallum T = tented area A spacing of five to six feet per man affected the amount of physical effort required to dig a ditch and build a rampart. Modern military engineering data indicate that an infantryman could, on average, shift 0.5 cubic meters (17.66 cubic feet) of earth per hour.19 Each foot-length section of a V-section ditch five feet wide and three feet deep would have 7.5 cubic feet of earth, so a six-foot section would have 45 cubic feet of earth. If a Roman soldier could move about 20 cubic feet per hour, than it would take 2.25 hours (45/20 = 2.25) to dig his six-foot section of ditch. The exact digging time would be influenced by the type of terrain in which the soldiers were digging. If the up-cast was used for the rampart, a similar period of work might be required. Perhaps four-and-a-half hours of labor before a defensive fight was all a general could allow. The next matter was the intervallum, which had to be wide enough to allow for movements between the ramparts and tents without crowding the tented area. The intervallum 19 Peddie 1994, 151. 12 had to be proportional to the side of the square. The fraction chosen was 1/10th the length of the rampart’s inner face, which is equal to 1/8th the length of the intervallum’s inner margin. The inter-relationship of these fractions was inherent in the model (Fig. 2.2).20 The partition of space within the camp shows eight squares along the inner face of the intervallum and ten along the outside. Figure 2.2 Inter-relationship between vallum and tented inner area (Richardson 2004) This is the template for all later Roman camps and forts with slight changes to the details. It is a rectangle whose area (R) is defined by the inner face of the rampart, with the intervallum some fraction (1/f) of the square root of R. This is also 1/(f-2) of the square root of the area within the intervallum (A).21 Outside the rampart there was a short space (berm) and then a ditch. The width and height of the rampart, as well as the depth and width of the ditch, would vary according to 20 Richardson 2004, 6. 21 Richardson 2004, 7. 13 the situation. Below are the features of three possible prototype squares for 100 infantry (Table 2.1). Table 2.1 Camp models for a century (Richardson 2004) Lengths in feet: areas in square feet Side of Perimeter Area within Intervallum Side of Area within square per man rampart width tented area intervallum 100 4 10,000 10 80 6,400 120 4.8 14,400 12 96 9,216 125 5 15,625 12.5 10 10,000 Which option is best? A clue comes from the area (A) which comprised the area actually occupied by the tents (T) and the remaining space for storing kit and centurion’s tents (A – T). The area (T) was made a simple fraction of (A). Each infantryman was given 83.33 square feet of tent space in the first camp for which we have dimensions.22 The third option gives each man 100 square feet within the intervallum. If 5/6ths of this area were for his tent space, then he would have 83.33 square feet. This suggests we have an early model. This Republican camp paradigm begins with the perimeter and works back to the area per man. The paradigm is reversible and a camp engineer calculating area and dimensions from numbers of men would have followed these steps:23 1. Number of men, or units, x space allowance = T (total area of tents) 2. T x 6/5 = A (area within intervallum) 3. L (side of the square) = √A 4. I (width of intervallum) = 1/8th of the √A 22 Richardson 2004, 7. 23 Richardson 2000, 427; Richardson 2004, 7. 14 5. Rampart length of one side = L + 2I A cavalryman and his horse would require more space than an infantryman. In the Republican camp he was given four times the amount of space, making each cavalryman count as four infantrymen for calculating camp dimensions. This suggests that a cavalry squadron (turma) may have been originally comprised of 25 men and occupied the same space as a century.24 2.3 The Republican Camp of Polybius Polybius (ca. 200 – 118 BC), in Book VI of The Histories, gave a detailed account of the camp made by a consular army consisting of two legions and allies. He did not cite his source but could have acquired the information from a military manual or a competent officer. His description is empirical with no hint of principles and with dimensions simply stated in feet. He mentioned that this process of camp construction was invariably applied.25 The infantry comprised two legions, each of 4,200 men with an equal number of allies, while the cavalry comprised 600 legionaries and 1,800 allies organized in turmae of 30.26 The camp was a square with sides measuring 2,017 feet and an intervallum of 200 feet (20 inches within 1/10th of 2,017 feet). The area at the rampart was 282.5 actus quadrati, the area within the intervallum 181.6 actus quadrati, and the intervallum 100.9 actus quadrati. Within the intervallum, the men’s tents were laid out in orderly rows with units occupying separate areas (Fig. 2.3). 24 Richardson 2004, 7. 25 Polybius VI.26. 26 Richardson 2000, 426; Richardson 2004, 11. 15 Figure 2.3 The Polybian Camp (Richardson 2004) The whole camp was divided into three equal parts by two lateral streets.27 The main lateral street was the Principia (100 feet wide) and the lesser the Via Quintana (50 feet wide). Most of the troops camped below the Principia and the space allocations are detailed below (Table 2.2).28 Table 2.2 Space allocation in the Polybian Camp (Richardson 2004) Block Area Soldier type Numbers Area per man (square feet) per block (square feet) 1 10,000 Legionary Cavalry 30 333.33 2 5,000 Triarii 60 83.33 3 10,000 Principes 120 83.33 4 10,000 Hastati 120 83.33 5 13,300 Allied Cavalry 40 332.5 6 20,000 Allied Infantry 240 83.33 27 Richardson 2004, 12. 28 Richardson 2000, 426–427; Richardson 2004, 12–13. 16 The infantry appear to have been organized in basic units of 60, recombined in certain proportions:29 Triarii, 60-men units Principes, 120-men units Hastati, 120-men units Peditates Sociorum (allies), 240-men units Each legion consisted of 70 (4,200/60) basic units, probably representing centuries reduced from 100 to 60 men. The cavalry turma of 30 men may be an increase of five over the original of 25. A reduced number of 40 infantry per cohort would free up the space for up to 10 cavalry per turma.30 These changes may indicate a shift in Roman military strategy and the importance of cavalry in determining the outcome of a battle. 2.4 Larger Camps An integral feature of the Roman camp paradigm was that no man would labor upon or defend more than five to six feet of perimeter. Due to the geometric properties of a square, perimeter and area do not increase at the same rate (Table 2.3).31 Table 2.3 Geometric properties of a square Area Side Perimeter 4.0 √4 = 2.0 8.0 8.0 √8 = 2.8 11.3 16.0 √16 = 4.0 16.0 29 Richardson 2004, 11. 30 Richardson 2004, 11. 31 Richardson 2004, 8–9. 17 While the area is quadrupled, the perimeter is only doubled. This mathematical relationship meant that, as the size of an army and its camp or fort increased, the footage that each man was required to defend would decrease (Table 2.4).32 In practical terms, it allowed for more men to defend the perimeter, acting as reserves. Table 2.4 Camp area and perimeter in relation to the number of infantry (Richardson 2004) Centuries Men Area (square feet) Perimeter Perimeter per man 1 100 15,625 500 5 5 500 78,122 1,118 2.2 20 2000 312,488 2,236 1.1 40 4000 624,975 3,162 1 2.5 Calculating Camp Dimensions Calculating camp dimensions as the centuries increased was not difficult because each needed 10,000 feet within the intervallum. Ten-foot measuring rods or decempedae could be used to layout the camp efficiently, as the intervallum (A) would be 100 square decempedae (A = centuries x 100). The side of the square would be √A or ten decempedae.33 Consider a camp for five centuries. The side of the square would be √ (5 x 100) = 223 feet or 22.3 decempedae. The intervallum (1/8th of 223 = 28 feet) would be added to this, giving a dimension at the inner face of the rampart of 223 + (2 x 28) = 279 feet. The paradigm allowed for an easy calculation of large numbers of troops. Consider a legion of 4,000 men (40 centuries) and 250 cavalry (equivalent to 10 centuries) in terms of space needed. The side of the square within the intervallum would be √ (50 x 100) = 707 feet, or 70.7 32 Richardson 2004, 9. 33 Richardson 2004, 9. 18 decempedae. Add to this the intervallum (1/8th of 707 = 88.3 feet) for a total of 707 + (2 x 88.3) = 883.6 feet at the inner face of the rampart. There is no direct evidence that this calculation was ever made, but it is difficult to see how various sizes of camps could have been made without it. The Romans had access to Greek mathematics with a strong understanding of square roots, many of whose values had been previously determined by the Babylonians and Egyptians.34 An engineer with a table of square roots and measuring rods would have no problem with these types of calculations. Even more likely, the dimensions for various camps were layed out by a staff in tables and learned by the responsible officer.35 2.6 The Evolution of the Camp Paradigm The organization of the army and its order of battle underwent significant changes over the last two centuries BC. This reflected both tactical considerations and social realities. The process is not easy to reconstruct from the surviving fragments. Polybius writes that a legion consisted of 4,200 infantry and 300 cavalry except in special times of danger when a legion consisted of 5,000 infantry and 300 cavalry.36 Marius, around 100 BC, created a legion of 6,000 and turned the centuries consisting of 80 or 100 men into cohorts made up of only 60 men.37 Regardless of these changes, the camp paradigm could cope. The side of a square camp at the inner margin of the intervallum was the square root of the sum of all the space allocations for men (or units) and can be written as a general formula: 34 Richardson 2004, 9. 35 Richardson 2004, 9. 36 Polybius VI.26. 37 Keppie 1998, 63. 19 Side = √(s n m) where S = the space needed by a unit; be it century, maniple, or cohort N = number of such units, having converted cavalry into infantry equivalents M = the value by which the tented area is multiplied to give the space within the intervallum (referred to as the multiplier); 6/5 in the Polybian camp The intervallum, which was 1/8th the side of the square was added to this number to give the dimensions at the inner face of the rampart. 2.7 Influence of Land Surveying Technology The rectangular camp was set out from a point where two axes crossed at right angles. There is strong indication that the procedure was borrowed from land surveying techniques of the Greeks and possibly the Etruscans.38 In a typical Roman land survey, two long axes called the cardo maximus and decumanus maximus were set out at right angles using a groma, a staff bearing crossed arms set at right angles and from whose extremities plumb bobs were suspended (Fig. 2.4).39 From the baseline, a matrix of secondary lines (limites) was laid out in a regular pattern creating a grid of squares. The length of measure was the actus (120 Roman feet) and the area measure was the actus quadratus of 120 x 120 Roman feet. The plots, or centuriae, were normally 20 x 20 actus.40 The process was known as centuriation and was the professional responsibility of land surveyors, agrimensores, or gromatici. The application of agrimensorial technology in camp layout comes from Hyginus: On the main street, at the middle of the entrance to the praetorium, is the point called locus gromae, either because the crowd collects here, or because in the laying out of the bounds, when the iron-shod upright has been placed on the spot, the groma is put thereon, 38 Richardson 2004, 8. 39 Richardson 2004, 8. 40 Dilke 1971, 69–70. 20 that the gates of the camp may form the four quarters in range of the line. And the professional followers of this art are called gromatici for the reason given above.41 Figure 2.4 Reconstruction of a groma Another hint at the application of agrimensorial technology to Roman camp layout is the term decumanus. This term applies to both the long axis of survey and the posterior portion of the central axis of the camp. The final clue comes from the dimensions of subdivisions of the camp described by Hyginus. All dimensions are multiples or simple fractions of an actus or 120 feet (the standard land surveying unit). Whereas the Polybian camp was set out in decimal measures (10s and 100s of feet), the Hyginian camp was set out in strigae of 60 feet each, and hemistrigia of 30 feet each.42 While the calculations for laying out a camp may seem at first somewhat complicated, Roman mathematics could cope with it easily. Ancient Greek, Babylonian, and Egyptian 41 Hyginus XII, trans. Richmond. 42 Richardson 2000, 428. 21 mathematicians had long before worked out many aspects of geometry and arithmetic including multiplication, division, decimals, and square roots which would all be accessible to an educated Roman.43 By the time of the late Republic, Romans were using a special shorthand system with a duodecimal system of fractions based on twelfths, where one half was written as 6/12 and one quarter as 3/12.44 This system would have suited calculations in the 120 foot units of the actus, with a decempedae being 1/12th of an actus. 43 Richardson 2004, 9. 44 Richardson 2004, 9–10. 22 Chapter 3: The Camp of the Imperial Army 3.1 Organization of Imperial Army The army described by Hyginus is that of the Empire, a fully professional work force that, while retaining legions, replaced the allies with non-citizen auxiliaries organized in cohorts. The auxiliary units were either quingenaria (nominally 500 strong) or milliaria (nominally 1,000 strong) but were actually comprised of numbers that were the nearest multiple of 60 or 80 (i.e. 480). The cavalry turmae were combined into alae, which were both quingenaria and milliaria, but actually based on multiples of eight.45 There were also combined infantry and cavalry units known as cohortes equitatae (Table 3.1). Table 3.1 Composition of units in the imperial army (Breeze and Dobson 2000, 161) Unit Infantry Men/Century Cavalry Men/Turma Total in Unit Centuries Turmae Legionary cohors I 5 double 160 800 cohors II-X 6 80 480 Equites legionis 4 30 (32) 120 Auxiliary cohors ped. Quin. 6 80 (100) 480 (600) cohors ped. Mill. 10 80 (100) 800 (1,000) ala quingenaria 16 30 (32) 480 (512) ala milliaria 24 30 (32) (42) 720 (768) (1,008) cohors equ. Quin. 6 80 (60) 4 30 (32) 600 (608) cohors equ. Mill. 10 80 8 30 (32) 1,040 (1,056) 45 Richardson 2004, 26. 23 3.2 De Munitionibus Castrorum While the authorship and date of this manuscript has been debated, I.A. Richmond offers a possible date range from internal evidence. Richmond argues that the mention of the non-Roman Palmyreni and Brittones supply termini. The last epigraphical record of the Palmyreni occurs in AD 238 under Gordian III, and since they were always recruited from the same region, could not have lasted after the ruin of their community, Palymyra, 35 years later.46 The Britons were first levied under Trajan, and these British units first appear with the Caledonian activity of Antoninus Pius in AD 142-145. The book therefore falls within a period later than Trajan’s reign and before the middle of the 3rd century AD.47 Richmond leans towards an earlier date in view of the simple Imperial titles. Hyginus appears to have been commissioned to search the literature and explain to his master how to make a camp. He could not find the principles for laying out the rectangle, but reported a lot of detail on units and the space they required.48 The army had undergone many changes since the time of Polybius. There were new units and tents were now pitched back-to-back in rows 60 feet (0.5 actus) wide and called strigae. Each tent row occupied a depth of 30 feet known as a hemistrigium. Hyginus provided the space allocation for units along the hemistrigium in feet, revealing that each unit occupied a certain number of actus. The area a unit covered in actus quadrati was determined by taking the footage it took up along the hemistrigium and dividing it by four, as a hemistrigium is ¼ of an actus deep.49 46 Richardson 2004, 77. 47 Richardson 2004, 77-78. 48 Hyginus XLV. 49 Richardson 2000, 428; Richardson 2004, 25. 24 3.3 Aspect Ratio Unlike the Polybian camp, the camp of the imperial army was usually not square but rectangular. The ratio of length to width is referred to as the aspect ratio. According to Hyginus, the preferred aspect ratio was 2 by 3. He claimed that this was for ventilation purposes and to expedite the trumpet signal.50 Richardson argues that this is not the case, and that the real reason for this aspect ratio comes from the Roman quasi-reverence for numbers.51 The imperial camp usually fell between an aspect ratio of 2:3 and a square. Hyginus indicated that with broader camps, their lay-out approaches a square.52 The word “approaches” is significant because, with very few exceptions, imperial camp and fort rectangles have perimeters in which the long axis is one digit higher than the short axis (ie. 2:3, 3:4, 4:5, 5:6 and so on). Algebraically, imperial Roman camps conform to the rule n: (n+1).53 This progression approaches a square but never reaches it. In the time of Pythagoras, this ratio of n: (n+1) was known as the harmonic mean, and was redefined by Archytas of Taras around 400 BC.54 The square is a geometrically simple shape that fits the purpose of the army quite well, so why would the Romans use an aspect ratio of 2: 3? Richardson argues that this ratio was the closest to the golden section: a proportion imbued with mystical significance, on account of its aesthetic properties.55 The golden section is best described as a line so divided that the ratio of the short section to the long is the same as the long section to the whole. It is not a finite number, like pi, but expressed as .618 to the third decimal place.56 50 Hyginus XXI. 51 Richardson 2004, 21. 52 Hyginus XXI. 53 Richardson 2001, 171; Richardson 2004, 21. 54 Richardson 2004, 21. 55 Richardson 2004, 23. 56 Richardson 2001, 174; Richardson 2004, 23. 25 Richardson examined a sample of 93 camps mostly from England but also with examples from Wales, Scotland, and Israel (Table 3.2). Their dimensions were taken from published plans at the inner face of the rampart or, when necessary, from ditch crop marks.57 The data were then converted into actus and the aspect ratio found by dividing the lengths of the cardo and decamus by the difference between them. Thus: c = C/ (D-C) and d = D/ (D-C) Where C and D are the actual measurements, then c and d represent the aspect ratio values c:d. Table 3.2 Frequency of aspect ratios of Roman camps (Richardson 2001) Aspect Ratio % of sample Aspect Ratio % of sample 1:1 14 7:8 4 1:2 6 8:9 1 2:3 29 9:10 1 3:4 3 10:11 5 4:5 15 11:12 0 5:6 10 12:13 0 6:7 4 13:14 1 While not every camp revealed an exact whole-number ratio, nevertheless, the slightest adjustment to measurements produced whole numbers. The need for an adjustment to measurements may be explained by slight discrepancies given map scales or repairs blurring the original fort perimeter. Regardless, the adjustments fell within a reasonable observer error of 1%.58 An aspect ratio of 2: 3 was by far the most common (29%) with an aspect ratio of 4: 5 the second most frequent (15%).59 57 Richardson 2001, 173. 58 Richardson 2001, 173. 59 Richardson 2001, 173; Richardson 2004, 23. 26 On occasion, the aspect ratio of an imperial camp was not square and did not follow the n: (n+1) rule. This type of camp was called a “warship” due to their long, narrow shape that resembled military vessels. Only three of the camps examined by Richardson followed this style: Cawthorn C (1:3), Uffington 2 (3:5), Sills Burn S (3:8).60 The small number of camps falling outside the n: (n+1) aspect ratio does suggest a reverence and preference for harmonic proportions, as the three “warship” examples are simple enough proportions that could be used anywhere, but were rarely utilized. Richardson argues that the ancient Greeks and Romans may have been aware of the mathematical progression known as the Fibonacci sequence, named after the Renaissance scholar who is believed to have discovered it.61 The sequence begins with adding the 1/1 ratio of a square and the next simplest ratio of 1/2 which produces a ratio of 2/3. The 1/2 and 2/3 ratios are then added together to produce 3/5. The sequence continues until the golden section is reached at 34/55. Unfortunately, Richardson bases this argument from one example: the camp at Uffington 2 with a 3:5 aspect ratio.62 Camps or forts with an aspect ratio of 1: 2, or 2: 3 should not necessarily be taken as evidence for the sequence, as these ratios follow the n: (n+1) rule of the harmonic mean. There appears to be no Roman fort in North Africa that conforms to this sequence. Unless more “warship” style forts and camps produce ratios that fall along the Fibonacci sequence, the evidence behind this hypothesis is far too weak to confirm. 3.4 Calculating Dimensions of an Oblong Camp Each axis of a square is the square root of its area. Special formulae would be required to calculate the sides of an oblong camp. Hyginus indicates that they were not in the literature 60 Richardson 2004, 23. 61 Richardson 2001, 174. 62 Richardson 2001, 174. 27 available to him.63 Polybius mentions a formula that was used but does not give it.64 While these formulae remain unknown, it is possible to suggest two which may have been used. A rectangle with a ratio of n: (n+1) can be divided into a number of sub squares (Fig. 3.1). Figure 3.1 Sub-squares in rectangles with n:(n+1) aspect ratios If the long axis is the decumanus (d) and the short axis is the cardo (c), the aspect ratio is c: d. The number of sub squares would be c times d. If the area of the entire rectangle is A, then the area of each sub square is A/ (cd). The side of a sub-square is √ (A/[cd]). Therefore, the length of the short axis is c √ (A/[cd]) and the long axis is d √ (A/[cd]).65 Algebraically: D = d √(A/[cd]) and C = c √(A/[cd]) Where D = decumanus in actus; C = cardo in actus; A = area in actus quadrati and c: d is the desired aspect ratio.66 63 Hyginus XLV. 64 Polybius VI.26. 65 Richardson 2004, 23–24. 66 Richardson 2000, 425; Richardson 2004, 24. 28 For example, take the Polybian square camp with an area of 180 actus quadrati within the intervallum or sides of 13.41 actus. This is how it would be transferred from a square camp to an aspect ratio of 2:3: D = 3 √(180/2x3) = 16.43 actus and C = 2 √(180/2x3) = 10.95 actus. 3.5 Notional Cohorts We now turn back to an aspect of Roman military engineering from which there is much indirect but no direct evidence. There must have been a planning unit (or transformation in mathematical terms) which allowed different infantry and cavalry combinations to be handled simply when calculating camp areas. It was easy to transfer cavalry space requirements into an infantry equivalent. Unlike the cavalrymen in the camp of the Republican army who were allowed four times as much space as an infantryman, cavalrymen were allotted twice the space of an infantryman in the camp of the imperial army. Simply doubling the total area taken up by the cavalry gave the space requirement for a cavalry unit in terms of infantrymen.67 Notional cohort numbers allowed infantrymen and cavalrymen to be treated as a common currency with regard to space allowance in a camp. Using dimensions provided by Hyginus in De Munitionibus Castrorum, Richardson was able to reason out several units’ space requirements in actus quadrati as well as the proportion of space needed, compared to an infantry cohort or notional cohort number (Table 3.3).68 Below are the spatial requirements of several different unit types as derived from Hyginus: 67 Richardson 2004, 26. 68 Richardson 2000, 428. 29 Infantry cohort: The legionary infantry had eight men per 12 feet of hemistrigium, or 1.5 feet per man, giving each 1.5 x 30 = 45 sq. feet (0.003125 actus quadrati). A century (80 men) took up 1 actus of hemistrigium, so occupied 0.25 actus quadrati. A cohort of six centuries (480 men) had 1.5 actus quadrati, much less than in the Polybian camp. Table 3.3 Space allowances in camps derived from Hyginus (Richardson 2004) Unit Hemistrigium Strigae Strigae Infantry-cohort (feet) (actus) (actus quadrati) equivalent Infantry century 120 1 0.5 0.25 Infantry cohort 720 6 3 1.5 1 Ala quingenaria 480 1,440 12 6 3 2 512 1,356 13 6.4 3.2 2.13 Ala Milliaria 720 2160 18 9 4.5 3 768 2304 19.2 9.6 4.8 3.2 1008 3024 25.2 12.6 6.3 4.2 Cohors equ. quin. 900 7.5 3.75 1.875 1.25 Cohors equ. mill. 1608 13.4 6.7 3.35 2.23 Ala quingenaria: Each cavalryman had 3 feet of hemistrigium, giving him 3 x 30 = 90 square feet (0.00625 actus quadrati) only twice that of the infantryman, not four times as much, as in the Polybian camp. When comprised of sixteen turmae of 30 men, it totaled 480, took up 12 actus of hemistrigium, and occupied 3 actus quadrati, equivalent to two infantry cohorts. If each turma had 32 men, with a total of 512 in the unit, then it would have taken up 12.8 actus and occupied 3.2 actus quadrati, equal to 2.13 infantry cohorts. 30 Cohortes equitatae: In the milliary unit, the infantryman had 1.2 feet of hemistrigium and occupied 1.2 x 30 = 36 square feet (0.0025 actus quadrati). The cavalryman had 2 (72 feet) to 2 1/4 more space giving him 81 square feet (0.0056 actus quadrati), so both had slightly less space than in the non-mixed units. Hyginus is quite explicit about the calculations in which he expresses the cavalrymen as infantryman equivalents. This unit, he writes, ‘has 240 horsemen which I reduce in infantry . . . by dividing by 2 and multiplying by 5 . . . so 240 becomes 120 . . . then multiplied by 5 equals 600. Subtracting the cavalry, there remain 760 men in the cohort which added to the result above, makes 1360.’69 By dividing by 2 and multiplying by 5 he indicates the cavalry had an infantry equivalent of 2.5. So 1360 x 1.2 feet of hemistrigium = 1632 feet (13.6 actus) giving 3.4 actus quadrati occupied space. If the officers took up another 48 feet of hemistrigium, this unit would occupy exactly 3.5 actus quadrati equivalent to 2 1/3rd infantry cohorts. The reduced space for mixed cohorts does not usually carry over to the fort paradigm. This produces a value of N = 1.5 for quingenaria equitata groups (480 infantry = 1, plus 120 cavalry = 0.5) and N = 2.66 for milliaria equitata groups (800 infantry = 1.66, plus 240 cavalry = 1). A legion would have a notional cohort number of 11.166, a milliaria first cohort of 800 men (N = 1.666) plus nine regular infantry cohorts (N = 9) and the cavalry component of 120 horses (N = 0.5) for a total of 11.166 (N = 1.66 + 9 + 0.5). The imperial infantrymen of the legions and non-mixed auxiliary units had 45 square feet of tent space compared to 83.33 square feet in the Polybian camp, or only 54% the amount of space. The cavalry in an ala had 90 square feet apiece, only twice as much as an infantryman, whereas a Polybian cavalryman had four times as much space as an infantryman or 333 square feet, only 27% the amount of space.70 The 69 Hyginus XXVI. 70 Richardson 2004, 26. 31 evidence suggests that the infantry in the mixed cohors equitata groups had a space reduction to 36 square feet with the cavalry component only having 72 to 81 square feet in the Roman imperial camp, but this reduction in space for mixed equitata units does not usually appear to transfer over to the Roman fort paradigm. These changes must have reflected the professionalization of the imperial army. The tighter packing of soldiers into smaller quarters represents the improved training and organization of the imperial army over its Republican predecessor. Having more men per unit area greatly increased the number of men available to make and man the defenses. More troops would have been available to take an active role in patrolling, foraging, and engaging the enemy.71 These changes would have greatly enhanced the army’s effectiveness. 3.6 The Multiplier in the Hyginian Camp Hyginus implies that he is describing a camp 12 by 18 actus or 216 actus quadrati in area, which was for three legions with auxiliaries. Below is a breakdown of the Hyginian army by total men and area of strigae needed (Table 3.4). The area of strigae was about 162 actus quadrati. This is ¾ of total area (216 actus quadrati), so the multiplier in the Hyginian camp was 4/3 (1.333).72 The area within the intervallum (A) was 1/3 bigger than the area of strigae, leaving room for roads, offices, workshops, and storage. Since each notional cohort had 1.5 actus quadrati of strigae, it accounted for 2 actus quadrati (1.5 x 4/3) within the intervallum (A). To calculate the area for an imperial camp, the praefectus castrorum would merely double the notional cohorts.73 All that was needed was the notional cohort number of each unit and the total number of units. Therefore, the army of 71 Richardson 2004, 26. 72 Richardson 2000, 429–430; Richardson 2004, 28–29. 73 Richardson 2000, 432; Richardson 2004, 29. 32 Hyginus with total notional cohorts of 108 would need 216 actus quadrati within the intervallum.74 Table 3.4 Troop numbers and space uptake in the Hyginian camp (Richardson 2004) (Strigae in actus quadrati: N = notional cohorts, strigae/1.5) Military Units Infantry Cavalry Type Number Men Strigae Men Strigae N Legions 3 15,360 48 32 Vexillarii 1,600 5 3.33 Misenum fleet 500 1.6 1 Ravenna fleet 800 2.5 1.66 Cohortes milliariae peditatae 3 2,400 7.5 5 Cohortes quingenariae peditatae 3 14,400 4.5 3 Cohortes Praetoriae 4 1,920 12 8 Statores 160 0.5 0.3 Legionary cavalry 360 2.25 1.5 Alae quingenariae 5 2,400 15 10 Alae milliariae 4 2,880 18 12 Praetorian cavalry 400 2.5 1.66 Scouts 200 1.25 0.8 Singulares 450 2.81 1.9 Palmyrenes 500 3.1 2 Gaeticulae 900 5.63 3.75 Brittones 500 3.13 2.08 Cantabri 700 4.38 2.92 Mauritanians 600 3.75 2.5 Pannonians 800 5 3.33 Cohortes equitatae milliariae 2 1,600 4 480 2.7 4.5 Cohortes equitatae quingenariae 4 1,920 4.8 480 2.7 5 Totals 27,700 90.36 11,650 72.21 108.4 74 Richardson 2004, 29. 33 3.7 The Intervallum of Imperial Camps Hyginus reports an intervallum width, the open space between the ramparts and tented area, of 60 feet for his army. This simply cannot be possible for an army of 40,000 men and 15,000 horses. The intervallum of the Polybian camp was 1/8th √A and a mathematical analysis of the intervallum at Masada B in Israel suggests it was the same (Table 3.5). The intervallum of the Hyginian camp would then be a much more believable width of 220 feet at 1/8th √216 actus quadrati, making the area within the rampart 337 actus quadrati.75 Table 3.5 Base rectangle areas and intervallum widths of the Masada camps (Richardson 2000) (A = base rectangle area, c = correlation coefficient) Camp A √A (actus quadrati) Intervallum c (actus) F1 12.25 3.50 0.38 B 10.62 3.26 0.28 C 2.43 1.56 0.12 F2 2.30 1.52 0.20 A 1.58 1.25 0.00 D 1.20 1.09 0.08 0.94 3.8 Acreage of Imperial Army Camps Because the model is linear, the number of notional cohorts relates closely with the area at the inner face of the rampart. The correlation in terms of acreage is notional cohorts (N) = acres/0.981 (Table 3.6).76 This relationship is important due to the use of over-the-ramparts measurements at many Roman camps which were measured in acres. Since one actus quadratus = 0.3215 acres and the Hyginian camp would have been 337 actus quadrati at the rampart with a 1/8th √A, it would produce a camp of roughly 108 acres at the rampart. There are at least three 75 Richardson 2000, 430; Richardson 2004, 30. 76 Richardson 2000, 431–432; Richardson 2004, 30. 34 similar camps in Scotland, at Normandykes (106 acres), Muiryfold (109 acres), and Kintore (110 acres).77 Table 3.6 Relationship of cohort equivalents to base rectangle and area over the rampart (Richardson 2000) Cohorts Base rectangle Area at inner face Area over the rampart of rampart (actus quadrati) (actus quadrati) (acres) (hectares) 5 10 15.6 5.4 2.2 10 20 31.2 10.4 4.2 20 40 71.7 23.4 9.5 30 60 93.7 30.4 12.3 40 80 125 40.3 16.3 60 120 187.5 60.3 24.3 80 160 250 79.7 32.3 100 200 312.4 99.4 40.2 140 280 437.5 138.7 56 180 360 562.4 177.9 72 3.9 Partition of Space and Summary of Imperial Camp Model There is the question of how rigidly the paradigm was applied to all situations. The camp area may have been increased over what the camp paradigm called for if large numbers of prisoners, livestock, or booty were captured. An increase in area had implications for manning the defenses. There is good reason to believe that the paradigm could handle storing prisoners and booty in most situations, as over a third of the area within the rampart was intervallum.78 Polybius writes, Again, all cattle brought into camp, as well as booty of all sorts taken from the enemy, are deposited in this space (intervallum) and securely guarded during the night-watches. 77 Jones and Society of Antiquaries of Scotland 2011, 102–103; Richardson 2004, 30. 78 Richardson 2004, 32. 35 But the most important use of this space is that, in night assaults, it secures the tents from the danger of being set on fire, and keeps the soldiers out of the range of the enemy’s missiles; or if a few of them do carry so far, they are spent and cannot penetrate the tents.79 Although the primary function of the intervallum was to organize defense and defend against enemy missiles, Polybius makes it clear that a certain amount of space was available as storage space. The paradigm for the Hyginian camp may be summarized thus:80 1. N = notional cohort number 2. S (strigae in a.q.) = N x 1.5 3. A (area within the intervallum) = S x 1.333, or A = N x 2 4. I = (√A)/8 5. The area at the inner face of the rampart (R) = (√A + 2I) 79 Polybius VI.31. 80 Richardson 2000, 431; Richardson 2004, 31. 36 Chapter 4: Forts, Fortlets, and Fortresses 4.1 Fort Definitions and Measurements Roman forts were designed as more permanent structures, but they were conceptually the same as a temporary marching camp: an outer rectangle defining the inner face of the rampart (R) within which the intervallum (I) surrounded an inner rectangle (A) that contained buildings. A fort was designed for auxiliary units with notional cohort numbers greater than or equal to one (N ≥ 1). Fortlets were conceptually the same as a fort but were designed to house cohorts or a number of soldiers less than or equal to one notional cohort (N ≤ 1). Fortresses were designed to house legions. Before exploring Richardson’s model for determining garrison type from fort dimensions, a quick overview of some features of Roman forts in North Africa and Britain strengthens some claims proposed by Richardson from his work on camps. Much like Richardson’s study of camps in Britain, the measurements of 2nd-century-AD Roman forts and one fortress, located mostly in Numidia, conform closely to the duodecimal system featuring fractions of an actus (Table 4.1). Table 4.1 North African fort measurements in actus Fort Measurements Gemellae 5 4 Thabudeos 3 1/6 2 1/12 Ad Piscinam 1 3/4 2 Mesarfelta 2 1 7/12 Djebel Mellah 3 1/3 2 1/6 Lambaesis (square) 5 1/3 5 1/3 Lambaesis (de l'est) 3 11/12 3 1/6 Lambaesis (fortress) 13 1/4 11 1/6 Ad Majores 4 1/2 2 11/12 Rapidum 2 2/3 2 2/3 37 Most measurements fell exactly on the corresponding fraction, while the others required very little adjustment (between 0.01 and 0.04 actus). The fractions are presented in simplest form, but all are divisors of twelve and under the duodecimal system the Romans would have written 1/3 as 4/12 and 3/4 as 9/12. 4.2 Aspect Ratio Evidence obtained from a study of 93 camps throughout Britain indicated that the Romans preferred their camps to be square or conform to an n: (n+1) aspect ratio. Aspect ratio is the relationship between the length and width of the sides of a rectangle. Thus, a fort measuring 300 x 200 meters would have an aspect ratio of 2:3. A sample of 41 forts in North Africa also conforms to the n: (n+1) aspect ratio (Table 4.2). Table 4.2 Frequency of aspect ratios in North African forts Aspect Ratio % of sample Aspect Ratio % of sample 1:1 31 7:8 2 1:2 2 8:9 0 2:3 22 9:10 5 3:4 15 10:11 5 4:5 7 11:12 0 5:6 7 12:13 0 6:7 2 17:18 2 In general, the sample of forts in North Africa conforms closely to the results seen in Richardson’s sample of camps. The three most common ratios for Richardson’s sample are 2:3, 4:5, and 1:1 (square), whereas the North African sample produced 1:1 (31%), 2:3 (22%), and 3:4 (15%) as the most common ratios (Fig. 4.1). 38 Figure 4.1 Comparative plans of 2nd and 3rd century forts and aspect ratios (Breeze et al 2013) Gemellae) 4:5, Rapidum) square, Thamusida) 7:8?, Gheriat al-Garbia) 3:4, Ad Majores) 2:3, Ausm) 2:3?, Talalati) square, Castellum Dimmidi) not applicable It is important to note that all but three of the square forts are dated to the 3rd century AD and later, suggesting that the reverence for or understanding of harmonic aspect ratios may have subsided by this time. Aspect ratios of 2:3 and 3:4 were by far the most common seen in 2nd century AD North African forts from the sample above. 4.3 The Intervallum Width of Forts An investigation of 14 forts throughout Britain indicates that the fort intervallum was typically 1/18th the square root of the area at the inner face of the rampart (R) and 1/16th of the square root of the area within the intervallum (A), but there was some variation (Table 4.3). 39 Table 4.3 Intervallum width as a fraction of the area it defines in Roman forts (Richardson 2002) (I = intervallum, R is the area by its outer margin and A by its inner margin) Fort I (feet) R I (actus)/√R A I (actus)/√A Gelligaer 20 9.33 0.0546 7.4 0.0613 Valkenburg 20 10 0.0535 8 0.0598 Oberstimm 20 10.41 0.0524 8.3 0.0587 Osterburken 33 16.45 0.0678 12.1 0.0791 Halton Chesters 21 10.93 0.0523 8.8 0.0582 Birrens (Antonine) 24 12.73 0.0561 10 0.0632 Wallsend 20 10.71 0.0509 8.7 0.0565 Pen Llystyn 14 11.4 0.0346 9.9 0.0371 Housesteads 34 14.35 0.0748 10.2 0.0887 Fendoch 30 12.25 0.0714 8.8 0.0843 Chesters 21 14.71 0.0456 12.1 0.0503 S Shields (Antonine) 19 12.11 0.0455 10 0.0501 Vindolanda 2 24 12.29 0.057 9.5 0.0649 Caerhun 20 12.49 0.0472 10.2 0.0522 Means 22.9 0.0545 0.0617 standard deviation 5.7 0.011 0.014 Fraction 1/18th 1/16th % error 2 1.3 Richardson determined that Roman camps utilized an intervallum width of 1/8th the square root of the inner area. It appears that forts were designed with an intervallum width of 1/16th the square root of the inner area, or half that of a camp. As will be shown, this mathematical progression continues onto legionary fortresses. 4.4 The Fort Model The creation of this model required the use of field observations and published reports of forts and camps in Britain, ancient texts, and inductive mathematical reasoning. It appears that instead of each notional cohort being given 2 actus quadrati within the intervallum, as in camp 40 layout, the space allowance varied between 6 and 8 actus quadrati per unit (rarely less than 6, but sometimes as low as 5 actus quadrati). The cohors equitata, who had a reduced space in temporary camps, was usually treated equally when in permanent quarters, as witnessed by the 1.5 notional cohort number that can be recognized at many equitata forts. The notional cohort number of an auxiliary unit for which a fort was intended can be found by dividing (A) by space allowances between 6 and 8 actus quadrati. This usually gives at least one recognizable notional cohort number, which may be regarded as the unit’s signature (Table 4.4). Table 4.4 Notional cohort values of units of the Roman army (Richardson 2002) (* If reduced space allowance applies) Unit Infantry Cavalry Notional value Area required (turmae) within camp intervallum legionary cohort 480 1 2 cohors quin. peditata 480 1 2 600-man cohors peditata 600 1.25 2.5 cohors quin. equitata 480 120 (4) 1.5 (1.25*) 3 (2.5*) 1st legionary cohort 800 1.67 3.33 cohors mill. peditata 800 1.67 3.33 ala quingenaria 480 (16) 2 4 cohors mill. equitata 800 240 (8) 2.67 (2.23*) 5.33 (4.5*) ala milliaria 720 (24) 3 6 A remarkable feature of this paradigm is that if one unit fits into a fort at 8 actus quadrati, the next biggest unit (by notional cohort number) fits the same fort at 6 actus quadrati. For example, a fort with 10 actus quadrati within its intervallum would fit a cohors peditata quingenaria of 600 men (N = 1.25) at 8 actus quadrati (10/8 = 1.25) or a cohors peditata milliaria (N = 1.666) at 6 actus quadrati (10/6 = 1.666).81 81 Richardson 2004, 35. 41 Again, what appears to be contradictory evidence in regard to the association of fort dimensions and troop numbers actually represents a flexible model that allowed adaptations to each specific situation. The equations for calculating unit size from fort dimensions are as follows:82 1. Length x width at the inner rampart (in actus) = (R) a.q. 2. The intervallum (I) = (√R)/18 3. The area within the intervallum (A) = [(√R)-2I]2 4. The notional cohort number (N) = A/8, A/7, or A/6 4.5 Classifying Forts According to Unit Richardson first tried to classify auxiliary forts on the supposition that they were designed with a space allowance of 8 actus quadrati with the capability of fitting larger units at smaller space allowances. Although data from forts have revealed that the areas of Roman forts tend to form a continuous series instead of discrete categories, Richardson implies that this continuum might be due to scale errors in published plans blurring small dimensional differences between discrete groups.83 Richardson breaks down a sample of forts from Britain into ten categories.84 Again, the data set does form a continuous series, but the notional cohort signatures at space allowances between 6 and 8 actus quadrati reveal the unit the fort was designed for and the range of units that could be housed. The area (R) was determined from published plans, and the value for (A) was calculated on the basis of an intervallum of 1/18th √R.85 Probable notional cohort signatures are in bold. Again, this data set reveals the remarkable flexibility of the Roman 82 Richardson 2004, 35. 83 Richardson 2004, 37. 84 Richardson 2004, 38–42. 85 Richardson 2004, 37. 42 military system and that most forts were designed to fit two or even three types of auxiliary unit (Table 4.5).86 Table 4.5 Units housed by fort groups (Richardson 2004) (* indicates units that could be accommodated at between 6 and 8 actus quadrati) Fort Groups 1 2 3 4 5 6 7 Units cohors quingenaria peditata * * * 600-man cohort * * * cohors quingenaria equitata * * * cohors milliaria peditata * * ala quingenaria * * cohors milliaria equitata * * ala milliaria * A sample of Roman imperial forts dated to the 2nd century AD and later from Numidia, Tripolitania, and Mauretania also appear to have been constructed to house different size units at varying space allowances (Table 4.6). Probable notional cohort values are marked in bold. 4.6 Fortlets Fortlets are defined as forts for units of less than one notional cohort (N ≤ 1). The fort paradigm is still applied, but with more variance in intervallum widths.87 Due to the intervallum irregularities and the effect of measurement errors with small scale plans, Richardson has 86 Richardson 2004, 42. 87 Richardson 2004, 45. 43 suggested, on the basis of his study of British fortlets, that it would be unwise to rely on troop estimates of fortlets from the model when it conflicts with other evidence.88 Table 4.6 North African forts by group Fort and Group R N at given space allowances Data Source 8 actus quadrati 7 actus quadrati 6 actus quadrati Group 1 Djebel Mellah 7.56 0.75 0.85 1 Fentress Thabudeos 7.62 0.75 0.86 1 " Group 2 Kaputurbe 9.75 0.96 1.1 1.28 Cagnat Bondjem 9.79 0.97 1.11 1.29 " Group 3 Rapidum 11.66 1.15 1.32 1.54 Seston Thanamarusa Castra 12.16 1.17 1.34 1.56 Cagnat Group 4 Zerberet et Tir 13.12 1.3 1.48 1.73 Fentress Lambaesis (de l'est) 13.27 1.31 1.5 1.75 " Ad Majores 13.96 1.38 1.58 1.84 " Group 5 Turrebaza Turris 16.81 1.66 1.9 2.21 Cagnat Group 6 Gemellae 21.29 2.1 2.4 2.8 Fentress Remada 22.41 2.21 2.53 2.95 Cagnat Tingit 22.86 2.26 2.58 3.01 " Group 7 Lambaesis (square) 29.88 2.95 3.37 3.94 Fentress Group 10 El Gahra 129.1 12.75 14.57 17 Fentress Even with these shortfalls, it is unsurprising that fortlets in Britain and North Africa also seem to have held one or more centuries of 60 to 80 men at space allowances of 6 to 8 actus 88 Richardson 2004, 45. 44 quadrati (Table 4.7). The Numidian fortlets are dated to the 2nd century AD. While the evidence for the two fortlets at Ad Medias being 2nd century in date is tentative, they were each manned by approximately 120 soldiers. Table 4.7 Numbers of men in British and Numidian fortlets Fort Area R (A) Infantry Numbers Britain Hardknott 3.73 2.95 240 Caerau 1.95 1.5 124 (120) Castle Shaw 1.79 1.41 113 (120) Highstones 1.28 1.01 81 (80) Lantonside 0.69 0.54 43 Poltross Burn 0.31 0.25 20 Numidia Ad Piscinam 5.88 4.65 320 (80 x 4) Mesarfelta 3.36 2.66 160 (80 x 2) Ad Medias 1.68 1.33 106 2.05 1.62 130 4.7 Legionary Fortresses Legionary fortresses were more variable in area than forts, most likely due to the varying local politico-military circumstances that influenced administrative functions and storage. Data from legionary fortresses of Britain and Lambaesis suggest that legionary troops were allowed even more space per unit at a rate between 10 to 12 actus quadrati (Table 4.8).89 The increased space allotted to legionaries probably reflects their higher status, length of service, and space required for equipment. 89 Richardson 2004, 46. 45 Table 4.8 Legionary Fortresses in Britain and Lambaesis (Richardson 2004) (R = area at the rampart; A = area within the intervallum; M = space allowance) Fortress R A Intervallum (feet) M (actus quadrati) Data Source York 120 100 58 8.3 Richmond Exeter 128 113 40 9.5 Goodburn Usk 128 120 20 10 Frere Gloucester 137 121 36 10 Crummy Chester 150 132 43 11 Richmond Colchester 170 150 46 12.5 Crummy Caerleon 170 150 46 12.5 Johnson Inchtuthil 170 150 48 12.5 Johnson Lambaesis 149 131 35 11 Fentress Mean 150 134 40 11 model 162 144 45 12 Features of the legionary fortress at Lambaesis closely resemble those of the fortress at Caerleon. Both fortresses have proportionally narrower intervallum widths when compared to the other fortresses in this sample, suggesting that these two fortresses may indeed have been designed to contain more stores and administrative functions than the others. This idea is supported at Lambaesis by customs tariffs documents that were discovered nearby.90 The intervallum widths of fortresses were also more variable with the mean being 1/32nd √A, which falls into a progression with the intervallum fractions of forts at 1/16th and camps at 1/8th (Table 4.9).91 Interestingly, the first built, Colchester, is very similar to the last fortress built, Inchtuthil, which again implies that area variations were not due to time but local 90 Fentress 1979, 208–209. 91 Richardson 2002, 100. 46 conditions. Richardson suggests that the smaller fortresses may have had shorter intended life spans, or were meant to contain fewer stores and officials.92 Table 4.9 Intervallum width as a fraction of the area in legionary fortresses (Richardson 2002) (I = intervallum; R = area at outer margin; A = area at inner margin in actus quadrati) Fortress I (feet) R I (actus)/√R A I (actus)/√A Novaesium 52 184 0.0322 161 0.0345 Neuss 51 180 0.0315 158 0.0336 Lambaesis 35 171 0.0223 156 0.0233 Colchester 51 170 0.0326 149 0.0348 Caerleon 30 170 0.0189 157 0.0197 Inchtuthil 48 170 0.0307 150 0.0327 Chester 48 150 0.0327 150 0.035 Lauriacum 30 143 0.0209 131 0.0218 York 58 120 0.0441 99 0.0485 mean 44.5 162 0.0295 143.4 0.0315 standard deviation 10.4 0.008 0.009 fraction 1/34th 1/32nd % error 2.7 2.8 4.8 Manpower and Defense of Forts, Fortlets, and Fortresses Since forts, fortlets, and fortresses had more generous space allowances than camps, there were relatively fewer men to man the defenses due to the mathematical relationship between area and perimeter. At a space allowance of 8 actus quadrati, it would take about half of an auxiliary garrison’s strength to man the ramparts at five-foot intervals (Table 4.10).93 Each man at the rampart would have one replacement, but these reserves would have been mobile to rush to points of pressure. The fort paradigm ensured that there were reserves for times of defense, but 92 Richardson 2004, 46. 93 Richardson 2004, 47. 47 Roman forts were not like medieval castles and could fall to a determined enemy.94 Ala quingenaria forts would have been particularly vulnerable since it would require 90% of the garrison to defend the ramparts at five-foot intervals, leaving hardly any men as reserves. Table 4.10 Men needed to man the ramparts of forts, fortlets, and fortresses Unit/Men Garrison R (actus quadrati) Perimeter (feet) Men needed % of garrison Auxiliary Fort Cohors quin. peditata 480 10.1 1,527 305 64 600-man cohort 600 12.7 1,708 342 57 Cohors quin. equitata 600 15.2 1,871 374 62 Cohors mill. peditata 800 16.9 1,971 394 49 Ala quingenaria 480 20.3 2,160 432 90 Cohors mill. equitata 1,040 27 2,494 499 48 Fortlets 400 5 1,208 242 60 300 3.8 1,046 209 70 200 2.5 854 171 85 100 1.2 603 121 121 80 1 541 108 135 60 0.8 468 94 156 Fortress Legio III Augusta 5,120 150 5,904 1,181 23 As previously discussed, due to the relationship between perimeter and area, bigger forts would have been easier to defend. Fortlets would have been hard pressed to defend their ramparts.95 94 Richardson 2004, 48. 48 While the Roman attitude was to march out and take the field, the Romans certainly had an understanding of the defensive capabilities that influenced the fort paradigm. The mathematical relationship between perimeter and area also ensured legionary groups could defend the ramparts even though they were allowed a more generous space allowance between 10 and 12 actus quadrati. The paradigm ensured that the ramparts of the legionary fortress at Lambaesis could be manned by approximately one quarter of the garrison for times when much of the garrison may have had an assignment or patrol duties. 95 Richardson 2004, 48. 49 Chapter 5: The British and North African Frontier Forts under Hadrian 5.1 Hadrian’s Wall Hadrian’s Wall in Britannia was planned to be 76 miles long, running from Newcastle to Bowness (Fig. 5.1). At first it was a stone wall, 10 Roman feet wide for the eastern 45 miles, and a turf wall 20 Roman feet wide at the base along the western 31 miles. In front of the wall was a flat space or berm of 6 to 20 feet and then a V-shaped ditch averaging 27 feet in width and 9 to 10 feet in depth. Fortified gateways were placed every mile at mile castles with two turrets in between each. The purpose of Hadrian’s Wall was to separate the Romans from the barbarians.96 Much like the African Fossatum, the purpose of Hadrian’s Wall was to control movements in and out of the province. Defensively, it discouraged small raiding parties, provided a lookout, and a front line for operations in northern Britain and Scotland. Furthermore, much as in Numidia, the controlling of movements allowed custom dues to be collected efficiently.97 While no customs tariffs documents like those discovered at Zarai and Lambaesis have been found near Hadrian’s Wall, the main purpose of Hadrianic linear frontiers appears to be the improved collection of taxes between the British frontier and Scotland areas, which were involved in heavy trade.98 Since Hadrian’s Wall enjoyed a life of 300-plus years, some of the fort outlines may have been slightly altered from their original aspect ratio because of renovations. The occupying units also changed from time to time, but there is generally strong agreement between the prediction of 96 Breeze and Dobson 2000, 1. 97 Breeze and Dobson 2000, 40. 98 Grønlund Evers 2011, 10. 50 the paradigm and the attested unit from inscriptions (Table 5.1).99 The forts of Hadrian’s Wall fall into the first five groups of fort-type set out by Richardson. Figure 5.1 Hadrian’s Wall (Newcastle University) 99 Richardson 2004, 51. 51 Table 5.1 Notional cohort signatures of Hadrian’s Wall forts (Richardson 2004) Fort and Group R A N at given space allowances Predicted Unit Attested 8 a.q. 7 a.q. 6 a.q. Group 1 Great Chesters 8.6 6.75 0.85 1 1.13 c. quin. ped. Yes Group 2 Carrawborough 10.5 8.3 1 1.2 1.38 c. quin. equit. No Wallsend 10.7 8.5 1 1.2 1.41 c. quin. equit. No Halton Chesters 10.9 8.6 1.1 1.2 1.44 c. quin. equit. No Group 3 Rudchester 12 9.5 1.2 1.4 1.6 c. quin. equit. Yes Carvoran 12 9.5 1.2 1.4 1.6 c. quin. equit. Yes Group 4 Castlesteads 12.7 10.1 1.26 1.5 1.67 c. quin. equit. Yes Housesteads 14.1 11 1.4 1.6 1.8 c. mill. ped. Yes Chesters 15.5 12.2 1.5 1.75 2 ala quin. Yes Birdoswald 15.6 12.3 1.5 1.75 2 c. mill. ped. Yes Benwell 16.9 13.3 1.67 1.9 2.2 ala quin. Yes Bewcastle 17 13.4 1.68 1.9 2.2 c. mill. ped. Yes Bowness 17 13.4 1.68 1.9 2.2 c. mill. ped. No 5.2 Hadrian’s Wall Fortlets While the information for the fortlets of Newcastle, Burgh-by-Sands, and Drumburgh along Hadrian’s Wall is incomplete, their total areas preclude them from containing an entire unit (Table 5.2). These fortlets would have been able to house between 240 and 320 infantrymen, between 120 and 160 cavalry, or some combination of the two. Richardson lays out a convincing argument that part of the cavalry component of the cohors milliaria equitata (N = 2.66) 52 associated with Bowness was housed at nearby Burgh-by-Sands and Drumburgh.100 The total area within the intervallum of all three forts is 21.4 actus quadrati (13.4 + 4 + 4). This total area would take the full unit at 8 actus quadrati (21.4/2.66 = 8.0). The notional cohort division would be: Bowness 1.66 (800 infantry), Burgh by Sands 0.5 (120 cavalry), and Drumburgh 0.5 (120 cavalry). While dividing an auxiliary unit between forts is certainly uncommon, other examples from North Africa and Britain indicate that finding suitable ground for horses sometimes necessitated this division. Table 5.2 Hadrian’s Wall fortlets (Richardson 2004) (R = area within the rampart; A= area within the intervallum) Fortlet R A Space Allowance 8 7 6 Newcastle (a) 5.9 4.6 0.6 0.7 0.8 Newcastle (b) 3.8 3 0.4 0.4 0.5 Burgh-by-Sands 5.1 4 0.5 0.6 0.67 Drumburgh 5 4 0.5 0.6 0.67 5.3 The African Fossatum The African Fossatum in Numidia is divided into four sections (Figure 5.2, solid black lines). The easternmost section, extending east from Ad Majores, has been shown to be a road accompanied by forts but not a linear barrier as such.101 100 Richardson 2004, 52–53. 101 Cherry 1998, 47. 53 Figure 5.2 The Numidian Limes under Hadrian (Fentress 1979) The three remaining sections of the African Fossatum are basically the same in design: a mud-brick wall fronted by a V-shaped ditch (Fig. 5.3). One section of the fossatum is 37 miles in 54 length, referred to as the Seguia Bent el Krass, and is located just south of the Oued Djedi and the fort at Gemellae. Figure 5.3 Features of the Fossatum (Breeze et al 2013) A second section runs approximately 28 miles between Mesarfelta and Thubunae, cutting across southwestern access routes to the Aures Mountains. The third section is approximately 87 miles 55 long and encircles the eastern half of the Hodna Mountains.102 Narrow gateways were placed approximately every mile with towers intermittently placed, as some were grouped and others were spaced farther apart. Since the aerial survey of the African Fossatum by Baradez, there have been questions surrounding the date and function of the structure. Baradez believed the fortifications were Hadrianic in date and the function of the fossatum was defensive. He bases his conclusions on the following arguments:103 1. The plan of towers on the fossatum is almost identical with that of the towers inside the fort at Gemellae (inscriptions indicate the fort is Hadrianic). 2. This plan is also similar to that of the turrets on Hadrian’s Wall 3. Sections through the ditch show it to be similar in section to the ditch at Hadrian’s Wall. 4. Finds from this excavation included coins and pottery from Hadrian’s reign. 5. The conception of the linear frontier is Hadrianic. Van Berchem and Pol Trousset argue that the fossatum is a legal boundary rather than defensive and that it dates to the 3rd century AD.104 They believe the fossatum delineates the desert from the sown, or in other words, separates arable from non-arable land. This hypothesis seems acceptable until the section encircling the Hodna Mountains is considered. It simply does not separate the desert and the sown. As far as dating is concerned, Van Berchem argued that the coincidence of this boundary with the limites in the Notitia Dignitatum makes the structure contemporary with limitanei (peasant militia) established by Gordian III, while Trousset excavated a guard-post along the 102 Cherry 1998, 47. 103 Jean Baradez 1949, 154-155. 104 Trousset 1974, 65-67; Van Berchem 1952, 42-49. 56 Djebel Tebaga section of the fossatum that dated to the 3rd century AD.105 Interestingly, Trousset himself indicates there was a previous structure on which this guard-post was built, but ignores the existence of a previous structure when attempting to date the fossatum. It has been agreed now that the fossatum is indeed Hadrianic in date.106 The function of the fossatum still needs to be addressed since it lacks much in the way of defense and does not separate arable and non-arable land in all cases. Elizabeth Fentress and John Cherry put forth the same convincing argument: the purpose of the fossatum was to control movement into and out of North Africa (Fig. 5.4).107 Figure 5.4 Linear barriers and transhumant routes in the frontier-zone (Cherry 1998) 105 Trousset 1974, 65-67; Van Berchem 1952, 42-49. 106 Cherry 1998, 46–47. 107 Cherry 1998, 66; Fentress 1979, 114. 57 The reason for this control of movements becomes apparent when an examination of seasonal transhumant routes is coupled with the discovery of customs tariffs documents at Lambaesis and Zarai. The Romans were funneling seasonal herders to specific areas so that they could monitor them better and tax them more efficiently. 5.4 The Forts of the African Fossatum under Hadrian The dating of forts near the fossatum is difficult, as only one quarter of the forts in Numidia can be dated with certainty. Inscriptional evidence indicates that the Roman fort at Ad Majores dates to AD 104/105 and the Roman fort at Gemellae dates to AD 126.108 Other forts must be dated on typological grounds. The fortlet at Ad Piscinam, the first fort at Djebel Mellah, and the early fort at Thabudeos are believed to be 2nd century AD in date due to the lack of projecting towers or gateways with projecting towers seen at other forts of the early 3rd century or later in North Africa.109 The fossatum is also used to identify the dates of associated forts. Mesarfelta and Thubunae form obvious termini for the section of the fossatum in the Southwest Aures and are therefore contemporary. Fentress postulates likely road connections to identify other Hadrianic locations in Numidia (Badias, Vescara, and Zarai).110 She uses this information to create the limes under Hadrian (map 2, pg. 7). As will be shown, inscriptional evidence indicates that the strength of the Numidian garrison under Hadrian fits well with the map produced by Fentress (Table 5.3). 108 Fentress 1979, 104. 109 Fentress 1979, 102. 110 Fentress 1979, 111. 58 Table 5.3 Numidian Forts under Hadrian Fort R A Space Allowance Predicted Unit and whether 8 7 6 attested by other sources Mesarfelta/Djebel Mellah 10.92 8.64 1.08 1.23 1.44 coh. Quing. Equ. yes Lambaesis (east fort) 13.27 10.48 1.31 1.5 1.75 coh. Quing. Equ. yes Thabudeos/Ad Piscinam 13.35 10.45 1.32 1.51 1.75 coh. Quing. Equ. ? Ad Majores 13.97 11.04 1.38 1.58 1.84 coh. Quing. Equ. yes Gemellae 21.29 16.82 2.1 2.4 2.8 Ala quingenariae yes Lambaesis (square fort) 29.88 23.61 2.95 3.37 3.94 Ala millaria ? Except for the Trajanic auxiliary fort at Lambaesis (east fort), the forts from the table above had available dimensions and have been shown to be most likely Hadrianic in construction date, based on architectural, inscriptional, and literary evidence. 5.5 Summary of Numidian Forts with Recorded Dimensions The Roman forts at Mesarfelta and Djebel Mellah appear to have shared a similar history to that of the Roman forts at Bowness, Drumburgh, and Burgh-by-Sands, where the cavalry and infantry component of an equitata unit were stationed in separate forts in close proximity to each other. The Cohors VI Commagenorum equitata is associated with both forts through inscriptional evidence.111 It cannot be proven with certainty that the two forts are contemporary, but architectural style suggests they were both 2nd-century AD forts. Furthermore, the infantry component of the equitata unit (N = 1) would fit into the fort of Djebel Mellah perfectly at 6 a.q. The cavalry component (N = 0.5) would also fit into the fort at Mesarfelta at a space allowance of 6 a.q. When the inscriptional and architectural evidence is combined with Richardson’s 111 Fentress 1979, 89–90. 59 model, they strongly indicate that the forts were contemporary, with each housing a portion of the Cohors VI Commagenorum equitata. In addition to the inscriptional and mathematical evidence, there are strong indications in North Africa and Britain that the logistics of finding suitable ground for horses would override the standard operating procedures in some cases. Djebel Mellah is located on a high plateau overlooking the surrounding area, including the fort at Mesarfelta.112 I argue that the placement of the fort at Djebel Mellah was of strategic importance, but that the high plateau did not provide enough suitable ground for grazing, training, and deploying the horses. The logistics of the situation required two forts: Mesarfelta to provide suitable ground for the horses that would have been necessary for patrolling the fossatum, and Djebel Mellah to provide a strategic location as Hyginus tells us that the Romans tried to avoid overlooking hills when placing a camp.113 While this arrangement was not common, evidence from Hadrian’s Wall strengthens this claim further. The Roman forts at Birdoswald, Great Chesters, and Housesteads near the center of Hadrian’s Wall were manned by cohors quingenaria peditata. The geography near the center of the wall was a craggy area that could not provide suitable ground for a cavalry component.114 The fort at Bowness and the fortlets at Drumburgh and Burgh-by-Sands display a similar situation to Mesarfelta and Djebel Mellah. Bowness was placed at a strategic location, but geographically the marshy area could not support the cavalry component of the unit. Logistically, it was necessary to divide the unit to find suitable ground for the cavalry component of this force. One might wonder why peditata units were not placed in these strategic areas when there was not suitable ground for horses like the three forts at the center of Hadrian’s Wall. The need for more mobility to patrol and scout the areas around frontier forts is demonstrated by the 112 Fentress 1979, 90. 113 Hyginus LVII. 114 Breeze and Dobson 2000, 55. 60 fact that almost all of the forts on Hadrian’s Wall or associated with the African Fossatum are ala or equitata units. The peditata units were mainly utilized in the central craggy area in the case of Hadrian’s Wall, and associated with settlements in Numidia such as Theveste and Hadreanum that were not located on or just behind the fossatum. One of the auxiliary forts at Lambaesis, referred to as the ‘east fort,’ measures 148 x 120 m or 472 x 381 Roman, and was in use from AD 81 to the end of the third century.115 The aspect ratio produced from these measurements is very close to 3:4. The ‘east fort’ was a group four fort capable of taking from a 600-man cohort (N= 1.25) at 8 actus quadrati to a cohors milliaria peditata (N = 1.66) at 6 actus quadrati. Richardson’s model produces a signature of exactly N = 1.5 at 7 actus quadrati, which is that of a cohors quingenaria equitata. There is no direct inscriptional evidence from the site to suggest the type of unit that was actually housed at the ‘east fort.’ But when the surviving epigraphic evidence from Hadrian’s speech to troops at Lambaesis in AD 128 is combined with the accuracy of Richardson’s model in predicting troop size from fort dimensions in Britain, they strongly suggests that the Cohors II Flavia Afrorum quingenaria equitata was stationed here when the Legio III Augusta arrived.116 Thabudeos and Ad Picinam are another example of two forts in close proximity to one another, most likely housing a portion of an equitata unit. Unforunately, this connection is even more tenuous than the connection suggested at Mesarfelta and Djebel Mellah, as there is no inscriptional evidence to support the presence of an equitata unit. The forts at Thabudeos and Ad Piscinam have a combined signature of (N = 1.51) at 7 actus quadrati. This is the exact signature produced at the fort of Ad Majores at 7 actus quadrati, which was known to house the Cohors II 115 Fentress 1979, 94. 116 Speidel 2006, 67. 61 Hispanorum equitata during the Hadrianic period, suggesting a similar size unit may have been stationed at those two forts together. The fort at Ad Majores was constructed in AD 104/105 and measures 170 x 110 m or 548 x 352 Roman feet. These measurements produce an aspect ratio just short of 2:3. When Richardson’s model is applied to the Roman fort at Ad Majores, it produces results congruent with group four forts able to take a 600-man infantry cohort (N = 1.38) at 8 actus quadrati to a cohors milliaria peditata (N = 1.84) at 6 actus quadrati. The numerical value closest to one of the three signatures is N = 1.57 at 7 actus quadrati, indicating Ad Majores housed a cohors quingenaria equitata unit. Inscriptional evidence suggests that the Cohors II Hispania Equitata was stationed at the fort.117 Again, the model agrees perfectly with the inscriptional evidence, and now it can be further concluded that the Cohors II Hispanorum Equitata was quingenaria in strength. Gemellae is located near the center of the Seguia Bent el Krass section of the fossatum, but about three miles north. The fort occupies about 7.25 acres and was dated to AD 125/126 by Baradez from an inscription found on a statue base in the principia.118 The enceinte measures 190 x 150 m or 604 x 477 Roman feet. The Roman fort at Gemellae strengthens Richardson’s hypothesis that Roman camps and, by extension forts, were planned out in actus and utilized the n: (n + 1) aspect ratio. The Roman actus of 120 Roman feet planned out with an aspect ratio of 4:5 would create measurements of 600 x 480 Roman feet. This is within a few Roman feet of the 604 x 477 measurements recorded at Gemellae. Inscriptions indicate that the fort at Gemellae housed the Cohors I Chalcidenorum and later the Ala I Pannonorum. Richardson’s model agrees perfectly with the epigraphical evidence, 117 Fentress 1979, 97. 118 Baradez 1949, 100. 62 and helps to further define the type of unit associated with the fort. For example, an ala could be quingenaria or milliaria with units ranging from 480 to 1,040, depending on the size of turmae. Richardson’s paradigm reveals that the fort at Gemellae was planned as a group six fort that could house multiple units from an ala quingenaria (N = 2) at 8 actus quadrati to a cohors milliaria equitata (N = 2.66) at 6 actus quadrati. The results produced from the fort model at 8 actus quadrati (N = 2.1) suggest the Ala I Pannonorum was quingenaria in strength, and its turmae were organized in groups of 32 (N = 2.13), not 30 (N = 2). The other fort at Lambaesis measures 200 x 200 m or 636 x 636 Roman feet. The fort is square, so a harmonic aspect ratio does not apply. It falls into group seven forts that would house an ala milliaria (N = 3 to 4.2), but the measurements in Roman feet do not fit into the scheme of actus as a base measurement. A reason for this issue is demonstrated in the study by Janon that revealed the square fort at Lambaesis did not show any signs of occupation and was most likely built as a military exercise for Hadrian’s visit in AD 128. A dedicatory inscription at the middle of the fort further supports this idea.119 The integrity of the strigium, which was based on the actus, would not have to be considered if no soldiers were actually intended to be housed there. The success of Richardson’s model, supported by inscriptional evidence, in correctly identifying troop sizes from fort dimensions in two provinces containing linear frontier systems allows for a confident examination of troop distribution in these areas. 119 Janon 1973, 253-254. 63 Chapter 6: The Numidian and British Frontier Garrisons under Hadrian 6.1 The British Frontier Garrison According to Breeze and Dobson, the forts along Hadrian’s Wall and the Cumberland coastal forts comprised 31.8 (32) notional cohorts, the equivalent to a legionary army group (Table 6.1).120 Richardson notes that, if the garrison at Carvoran was a 600-strong cohors quingenaria peditata (N = 1.25), then the total garrison on the British frontier would be 32 notional cohorts. Although the data from Breeze and Dobson is mostly accurate, Richardson’s model has shown the Hadrianic fortlet at South Burgh-by-Sands could not reasonably house a cohors quingenaria equitata, and that Burgh-by-Sands most likely housed a portion of the cavalry associated with nearby Bowness. While referring to the larger Roman fort at Burgh-by-Sands (North), Breeze and Dobson even admit, “It should be noted however that recent excavations have failed to find a Hadrianic fort here.”121 Richardson missed this information, but when the totals are adjusted considering this revelation, the new total becomes 30.3 notional cohorts. Historical examples of legionary armies with auxiliaries equaling approximately 30 notional cohorts are provided by Josephus and Tacitus.122 Josephus describes a three-legion army with auxiliaries (N = 90.75) and a single legionary army with auxiliaries (N = 30). Tacitus describes a two-legion army of Agricola (N = 60).123 Richardson was correct in believing that Hadrian’s Wall and coastal forts were manned by the equivalent to a legionary army with auxiliaries, but he was slightly off in establishing the appropriate notional value for such a force. 120 Breeze and Dobson 2000, 54. 121 Breeze and Dobson 2000, 51. 122 Josephus II.498; Josephus III.71. 123 Tacitus Agricola, XXXV. 64 Table 6.1 The Garrison of the British Hadrianic Frontier (Breeze and Dobson 2000) Fort Unit Notional Cohorts Infantry Cavalry Totals Infantry only Newcastle cohors quin. ped. 1 1 Great Chesters " 1 1 Carvoran " 1 1 Beckfoot " 1 1 Birdoswald cohors mill. ped. 1.67 1.67 Bewcastle " 1.67 1.67 Housesteads " 1.67 1.67 Cavalry Only Chesters ala quingenaria 2 2 Benwell " 2 2 Stanwix ala milliaria 3 3 Mixed Units Wallsend cohors quin. equit. 1 0.5 1.5 Rudchester " 1 0.5 1.5 Halton Chesters " 1 0.5 1.5 Carrawborough " 1 0.5 1.5 Castlesteads " 1 0.5 1.5 Burgh-by-Sands " 1 0.5 1.5 Moresby " 1 0.5 1.5 Bowness cohors mill. equit. 1.67 1 2.67 Maryport " 1.67 1 2.67 Totals 19.35 12.5 31.85 6.2 The Numidian Garrison Hadrian’s speech at Lambaesis combined with John Spaul’s work on inscriptional evidence of auxiliary units produces a nearly identical notional cohort value of 30.4 for the Numidian garrison under Hadrian. The names of the units present at Hadrian’s speech at Lambaesis include the Legio III Augusta, Cohors II Hispania equitata, Cohors I Flavia equitata, 65 Cohors II Hamiorum, Ala I Pannonorum, and an unknown Ala group.124 Michael Speidel puts forth a hypothesis that the units recorded in Hadrian’s speeches to the African army are listed in the order Hadrian inspected them.125 Speidel’s hypothesis, combined with Spaul’s work on inscriptional evidence and Richardson’s model, produces a tentative distribution of troops throughout the Numidian frontier ca. AD 130 (Table 6.2). Table 6.2 Numidian Garrison, ca. AD 130 Unit Name Probable Hadrianic Location NCN Cohors VII Lusitanorum equitata Vazaivi (Ain Zoui) 1.5 Cohors I Flavia Hispanorum equitata Zarai 1.5 Cohors II Hispanorum equitata Ad Majores (Henchir Bessiarini) 1.5 Cohors II Gemella Thracum equitata Mascula (Kenchela) 1.5 Cohors VI Commagenorum equitata Mesarfelta (Auguneb) and Djebel Mellah 1.5 Cohors I Chalcidenorum equitata Thubunae? 1.5 Cohors II Flavia Afrorum equitata Thabudeos and Ad Piscinam? 1.5 Ala Flavia Badias? 2.13 Ala I Pannoniorum Gemellae (El Kasbat) 2.13 Legio III Lambaesis 12 Cohors II Hamiorum milliaria Theveste 1.66 Cohors I Syrorum Sagittariorum Vescara? 1 Cohors XV Voluntariorum (civium Romanorum) Ammaedara (Haidra) 1 Total 30.42 As previously mentioned, the dating of Hadrianic forts in Numidia is tenuous and the placement of some garrisons even more so. Even so, a force of 30 notional cohorts is almost identical to several legionary armies described by Tacitus and Josephus, as well as the notional 124 Fentress 1979, 96. 125 Speidel 2006, 49. 66 values produced by the probable frontier garrison of the British frontier. Hadrian’s Wall, along with the Cumbria coastal forts, and the Numidian frontier were manned by almost the same strength of troops (N = 30), which, as Josephus and Tacitus indicated, was equivalent to several different legionary armies with a complement of auxiliary units, suggesting each of these linear frontiers were managed as their own distinct military entity. 67 Chapter 7: Best-Fit Mixed Unit Model 7.1 Logic behind Model Evidence for the presence of mixed equitata units in the forts along both the African Fossatum and Hadrian’s Wall allows for the altered application of another formula created by Richardson: the Best-Fit Mixed Unit Model. Richardson developed this model to examine infantry-to-cavalry ratios in different camps with an equitata signature throughout Britain. My application of the best-fit model to forts in North Africa and Britain required a simple adjustment to the square feet allowed per man to account for the more generous space allowance of 6 to 8 actus quadrati per cohort in forts versus camps, in which the space allowance was only 2 actus quadrati per unit within the intervallum. The original logic, as well as my adjustments to the model, is as follows: Each infantryman had 45 square feet of space within the tented area (S), which is equal to the area within the intervallum (A) times the multiplier of ¾ in the imperial camp. Additionally, each cavalryman had twice as much space, or 90 square feet for rider and horse. So the total infantry that the strigae could hold was (S x 14,400)/45), because there are 14,400 square feet per actus quadrati. Since each cavalryman occupied the space of two infantrymen, the whole area per strigas (S) could be divided into 45 square foot “infantry space units” of which the infantryman would have one and the cavalryman two. If the relative proportion of infantry and cavalry in the camp is known, then the actual numbers of each could be calculated from the total space units.126 My adjustment to the model comes from the more generous space allowance given to soldiers when in permanent quarters. It stands to reason that if each infantryman is given 45 square feet of space within the area per strigas of a camp at 2 actus quadrati per cohort within the intervallum, then, at a fort where a cohort was allowed three times as much space at 6 actus quadrati within the intervallum, each infantryman would have three times as much space within the area per strigas as well, or 135 square feet. Therefore, the previous equation would switch 126 Richardson 2002, 106. 68 from (S x 14,400)/45 for a camp to (S x 14,400)/135 for a fort where the notional cohort signature of a unit was produced at 6 actus quadrati. If a recognizable signature for a unit occurs at 7 or 8 actus quadrati, then the denominator in the formula becomes 157.5 (45 x 3.5) or 180 (45 x 4) square feet. Also, the forts along Hadrian’s Wall in Britain have strong inscriptional evidence for equitata units, but do not produce the associated signature (N = 1.5). Richardson has suggested that some of the forts were originally designed for a peditata unit with the cavalry element being added after the perimeter had been set.127 This is not a totally unconvincing argument, but a closer look at the signature of (N = 1.2) produced by these forts may provide a more concrete answer. The forts at Carrawbrough, Wallsend, and Halton Chesters produce signatures of N = 1.38, 1.41, and 1.44 at a space allowance of 6 actus quadrati. These results are not that far short of the expected signature of N = 1.5 for a quingenaria equitata unit, but neither are they convincing. These three forts produce signatures for a peditata quingenaria unit (N= 1.0, 1.0, and 1.1) at a space allowance of 8 actus quadrati. This is likely the reasoning behind Richardson’s hypothesis that the forts at Carrawbrough, Wallsend, and Halton Chesters were originally designed for a peditata unit with the cavalry component added after perimeters had been set. Furthermore, the forts at Rudchester and Castlesteads were believed to house cohors quingenaria equitata units, but produce notional values not quite congruent with that of a cohors quingenaria equitata (N = 1.5). Rudchester produces a notional value of (N = 1.4) at 7 actus quadrati and (N = 1.6) at 6 actus quadrati. Similarly, Castlesteads produces a notional value of (N = 1.44) at 7 actus quadrati and (N = 1.67) at 6 actus quadrati. At a space allowance of 8 127 Richardson 2004, 52. 69 actus quadrati, both Rudchester (N = 1.2) and Castlesteads (N = 1.26) produce notional values closer to the expected (N = 1.23) signature of a quingenaria equitata unit with the reduced space allowance of 36 square feet per infantryman and 72 square feet per cavalryman in Roman camps. Although, as previously mentioned, the restricted space allowance for an equitata unit in the imperial camp did not usually apply to forts, Hadrian’s Wall forts may be the exception. Unlike the equitata forts in Numidia, when the best-fit model was applied to these five forts along Hadrian’s Wall with regular space allowances (45 square feet for infantrymen, 90 square feet for cavalrymen), it produced insignificant results. This led me to explore the possibility that the equitata forts along Hadrian’s Wall were designed with a reduced-space allowance seen in camps of imperial date, and recognize the reduced space signature (N = 1.23) of mixed equitata units. To test this reduced-space hypothesis, at the forts of Carrawbrough, Wallsend, and Halton Chesters, the denominator in the previous formula was changed from 157.5 for forts at 7 a.q. to 126 (36 x 3.5) at 7 a.q. Rudchester and Castlesteads require the denominator to become 144 (36 x 4) at 8 a.q., accounting for the reduced space allowance per man. Continuing with the original logic behind Richardson’s best-fit model: If, for example, there were three infantrymen for each cavalryman, then the infantry would have three out of every five space units and the cavalry would have two. That is, the proportion for the infantry would be 3/5, leaving 2/5 for the cavalry. Suppose there were 600 space units, then 360 (600 x 3/5) for the infantry and 240 (600 x 2/5) space units to the cavalry, which means the cavalry would number 120. Expressed algebraically, the number of infantrymen (I) is I = p x (r/[r + 2]) where p is the number of space units and r is the number of infantrymen per cavalryman. The number of space units (p) is derived from the previous formula of (S x 14,400)/45 for camps or 135, 157.5, and 180 for forts. The number of cavalrymen (C), expressed algebraically, would be C = (p – I)/2. A spreadsheet can be extended to calculate the numbers of both infantry and cavalry for any given infantry-cavalry ratio. Spreadsheets created from forts along Hadrian’s Wall and the African Fossatum use ratios from 1:1 all the way up to 20:1 infantry per cavalryman in stages of 0.1, which produces 200 permutations. The number of infantry (I) thus obtained, when divided by 480, gives the notional infantry cohorts and dividing the cavalry number (C) by 30 or 32 gives the number of 70 turmae. When, for a given ratio, both these notional infantry cohort and turmae numbers are nearly whole numbers (within 0.04), we have a plausible combination or best-fit.128 7.2 Best-Fit Results The results indicate both frontiers mainly utilized turmae of 30, but the forts for mixed quingenaria equitata units in Britain were designed with the reduced space allowance seen in imperial camps (N = 1.23), whereas the forts for mixed quingenaria equitata units in Numidia were designed with space allowances equivalent to those in camps of non-mixed groups (N = 1.5). The “best-fits” are summarized below (Table 7.1). Quingenaria equitata units of forts along Hadrian’s Wall produce significant results for the best-fit model at the reduced space allowance (N = 1.23), but indicate inconsistencies in the formation of turmae, with units of 30 and 32 being utilized. The forts in Numidia produce much more consistent results with only turmae of 30 at a space allowance of (N= 1.5). Table 7.1 Summary of Best-Fits for Equitata Forts Fort Ratio Infantry Cavalry Cohorts Turma (30) Turma (32) Space Allow. Numidia Ad Majores 4.00 481.3 120.30 1.00 4.01 3.76 7 a.q. (N = 1.51) East Fort 4.00 479.3 119.80 1.00 3.99 3.74 7 a.q. (N = 1.50) Thabudeos 4.10 489.3 119.3 1.02 3.98 3.73 7 a.q. (N = 1.51) Britain Rudchester 4.00 475.3 118.8 0.99 3.96 3.71 8 a.q. (N = 1.2) Castlesteads 3.90 500.3 128.3 1.04 4.28 4.01 8 a.q. (N = 1.26) Wallsend 3.70 473.2 127.9 0.99 4.26 4 7 a.q. (N = 1.21) Carrawbor. 4.00 474.8 118.7 0.99 3.96 3.71 7 a.q. (N = 1.22) Halton Chest. 3.60 473.8 127.6 0.99 4.25 3.99 7 a.q. (N = 1.23) 128 Richardson 2002, 106. 71 These results suggest that the designers of forts along Hadrian’s Wall and the African Fossatum were both utilizing a manual similar to what Hyginus produced, but with slight differences. It must be remembered that this phenomenon of reduced space for equitata forts only pertains to Hadrian’s Wall and not all of Britain, which has many quingenaria equitata forts that produce (N = 1.5) signatures. While the reasons are unknown, one may conclude that the designers of Hadrian’s Wall forts either mistakenly designed the forts at a reduced space, were working with a specialized manual or orders, or the approach to space allowances for equitata units changed between the construction of the forts along Hadrian’s Wall and those located near the African Fossatum. Regardless of the reason for the equitata forts along Hadrian’s Wall being designed with a reduced space allowance, my creation and application of a “best-fit” model for Roman forts indicates that Richardson’s model for calculating garrison size from fort dimensions is more accurate than he realized. In Chapter Five, inscriptional evidence indicated that Richardson’s model was incorrect in predicting garrison size from fort dimensions for five forts along Hadrian’s Wall (Table 5.2). My best-fit fort model indicates that Richardson was actually correct on all counts when the reduced-space signature of (N = 1.23) for mixed equitata units is recognized at these forts. If the cavalry component of the garrison associated with Bowness was stationed at the nearby fortlets of Drumburgh and Burgh-by-Sands, Richardson’s fort model accurately predicts the garrison size from dimensions for all forts associated with Hadrian’s Wall and the African Fossatum. 72 Chapter 8: Conclusions Richardson’s research indicates that the Romans approached the organization of their armies and problems of camp and fort design with a sound understanding of ergonomics; that is, with a grasp of the quantifiable aspects of a soldier’s effort in both terms of manual labor and combat. They also seem to have understood a variety of other aspects for which we must use modern terms, such as man-hours, work rate, and optimum deployment of resources.129 The Romans used mathematics to manipulate these aspects into a workable paradigm. Besides using simple addition, multiplication, squares, and square roots, the Romans applied what we now call transformations to avoid calculating large numbers, while working towards the mathematical ideas of harmony discovered by the Greeks. This methodology seems to have formed the core of their military science from the Republic to the end of the western Empire. This information must have formed what we would call standard operating procedures and would be used to train gromatici and those aspiring to the rank of praefectus castrorum, many of whom became agrimensores after their service.130 The military engineer and his knowledge seems to be taken for granted, up to the point that the methodology was lost. The model also suggests that both the British and Numidian frontiers were manned by the same number of troops (N =30), equivalent to a legionary army with its full detachment of auxiliaries. Historical sources also indicate that an army with a notional cohort equivalent of 30 was utilized at various times during the Imperial period. This evidence suggests that these linear barriers, associated forts, and troops were viewed and handled as a distinct entity from the rest of the surrounding province. Although Hadrian’s Wall and the African Fossatum were quite 129 Richardson 2004, 67. 130 Richardson 2004, 67. 73 different in length and construction, it appears that Hadrian viewed each as a single unit. Future research is required to see if other Hadrianic linear barriers conform to this notion. The best-fit model indicates that the equitata forts along Hadrian’s Wall were designed at a different space allowance than the forts near the African Fossatum. This realization would never have come about without the creation of my best-fit model for forts. By testing the best-fit model on equitata forts along Hadrian’s Wall, I was able to determine that these equitata forts were designed at the reduced space allowance seen in imperial camps of equitata units. It cannot simply be regional variation, since other equitata forts in Britain do not conform to the reduced-space rule and produce signatures of (N = 1.5) like the equitata forts in North Africa. I can only speculate that it was a mistake or the specific instructions given to the fort engineers along Hadrian’s Wall. Roman camps were designed with a standardized manual that allowed a degree of variance to adapt to almost any circumstance that arose. The model could deal with unsuitable ground, extra supplies or booty, and through the multiplier allow a wide range of possible administrative layouts adjusted to each geo-political situation. There were certainly conditions under which the standard operating procedures were abandoned. 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Thesis/Dissertation
eng
Ancient Culture, Religion and Ethnicity
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Theoretical approaches to Roman camp and fort design : an examination of the frontiers in Britain and North Africa under Hadrian
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