The commonest estimate for the overall population of the empire under the Principate is some sixty million. This is almost certainly far too low, based on pessimistic assumptions about life expectancy and the maximum population able to be supported by agriculture over a given area. Year by year archaeologists identify more and more settlements from the immediate pre-Roman and Roman periods, aided by improvements in the techniques and technology of surveying. It is early days, but over time this is likely to lead to higher figures for populations in this period. Even if we accept sixty million as a working total, then by the end of the second century there were more than 170 civilians for every soldier. The ratio was certainly higher in the first century AD and probably throughout the period, since not only is the population likely to have been considerably larger, but the evidence suggests that most of the time army units were substantially below their theoretical strength.3
At no stage was the army evenly distributed throughout the empire, so that in fact the soldier-to-civilian ratio varied over time and from region to region. Tacitus in his account of AD 23 gives a convenient survey of the disposition of the legions at that time. The ‘main strength’ of eight legions was on the Rhine, while there were two each in the Danubian provinces of Pannonia and Moesia, backed by two more in neighbouring Dalmatia. Four were in Syria, three in the Spanish provinces, two in Egypt and two in Africa. This deployment reflected the main areas of military activity of Augustus’ reign, with concentrations of troops in recently conquered territory such as Egypt, Spain and especially the Balkan provinces. The legions in the Rhineland stood ready to defend against attacks from the Germanic tribes or to advance if the emperor ever decided to renew the attempt at conquest. Tacitus notes that they were equally well placed to deal with trouble in Gaul, as they showed in the rebellion of Florus and Sacrovir. Deployments were not rigid. Later in the first century one legion in Upper Germany was moved west from the Rhineland for several decades, before once again being shifted back nearer the frontier. The strong army in Syria helped to control an area disturbed during the civil wars and the Parthian invasion in the last decades of the Republic.4
Priorities changed over time. The presence of two legions in Africa in AD 23 was short-lived, prompted by the struggle with Tacfarinas, a former auxiliary-turned-war leader who raided the settled province for several years. Before he was defeated the extra unit was withdrawn, and then for centuries the area was held by a single legion, Legio III Augusta, supported by auxiliaries. The Spanish Peninsula was also soon considered to be more secure, and its garrison was reduced to one legion, as eventually was the garrison of Egypt. Claudius sent four legions to conquer Britain, and three were considered necessary to occupy it from the end of the first century AD. Around the same time, units were shifted from the Rhine to the Danube, and the Rhineland garrison was halved to four legions, a pair in each of the two German provinces. There were ten legions in the Danubian provinces for most of the second century AD. Another marked increase was in the eastern provinces, where the total rose to eight legions in Cappadocia, Syria, Judaea and Arabia. At times provincial armies were reinforced by shifting troops from other provinces. There was no central reserve of legions, since the slow speed of movement made the idea impractical, which meant that units were deployed where it was thought that they were needed.5
Most of the army was on or near the frontiers of the empire. In the second century AD the orator Aelius Aristides claimed that the Romans ‘did not neglect walls, but put these about your empire, not your city. And you erected them as far off as possible . . . just as a trench encircles an army camp.’ A little earlier, Appian expressed a similar idea, saying that the Romans ‘surround the empire with great armies and garrison the whole stretch of land and sea like a single stronghold’. A hundred years later another Greek author claimed that Augustus ‘established a defensive system of forts’ garrisoned by salaried professional soldiers ‘to act as a barricade for the Roman Empire’. This scarcely reflected the decades of expansion under the first princeps, but is revealing of the ideals of the third century AD.6
Yet the Roman army was not structured to act as a static defensive force. Under Augustus, the bulk of the army spent the spring and summer under canvas, operating in the field on manoeuvres if not active campaigning. Then for the autumn and winter, in a way familiar to Caesar and Cicero and earlier generations of Roman commanders, it returned to hiberna or winter quarters. In settled, urbanised provinces, troops were sometimes billeted in cities as they had been under the Republic – something usually impossible to trace in the archaeological record. Otherwise they constructed fortified camps and timber buildings for accommodation. In Gaul, Caesar’s legions rarely returned to the same place for successive winters. Under Augustus this became more common, especially along the Rhineland, so that the hiberna became more permanent and more solidly built, their basic design followed throughout the empire. Camps were sited to make best use of the emerging road system and transport of men and supplies by water. Unless the local situation changed dramatically, or the unit was transferred to another province, there was little point in shifting the site of a garrison and undergoing the cost and effort of creating a new camp. Over time, winter quarters turned into long-term bases, housing the unit’s headquarters and records, workshops and other facilities. Even so, these bases were where the army lived when it was not required for active service or the many other tasks soldiers were called upon to perform, and were not places where it expected to fight, unless the situation was dire. Looking at a plan of such a camp it is the barracks, officers’ houses, granaries and other buildings that dominate rather than the fortifications.7
A legion was designed as a force for fighting pitched battles. Its basic tactical unit was the cohort, with a paper strength of 480 men, and there were ten of these in each legion. At some point during the first century AD some legions increased their first cohort to number 800, and it is possible that the soldiers in this unit were taller or more experienced. A small cavalry force of 120 men acted as escorts for senior officers, as scouts, despatch riders, and could also serve as a formed unit. Otherwise all ten cohorts consisted of close-order infantrymen, protected by helmet, long shield and body armour – sometimes supplemented by greaves and articulated armour for the right arm. Offensive weapons consisted of the pilum – a heavy throwing javelin with an effective range of some fifteen yards – backed up by the well-balanced cut-and-thrust sword, the gladius, with a blade measuring between 20 and 24 inches. Even in defence, the classic tactic was to throw the pilum and follow this up with a charge sword in hand. As well as protecting the body from shoulder to knees, the heavy shield was designed to be used aggressively, punching an opponent with the dome-shaped metal boss to unbalance him and lay him open to the thrust of the sword.8
In support of the legions, the auxilia provided substantial numbers of well-mounted, disciplined cavalrymen – something often lacking under the Republic – as well as archers equipped with sophisticated composite bows. There were also slingers and other skirmishers, but the majority of auxiliary infantrymen fought in a style very similar to the close-order legionaries. They did not employ the pilum or carry the semi-cylindrical body shield – nor is there evidence for auxiliaries using the famous banded armour known today as lorica segmentata, but this was never universally worn by legionaries either. Instead auxiliaries had long, flat shields and carried a range of spears and javelins. They all wore helmets and a cuirass of mail or scale, so that it is a mistake to see them as ‘light infantry’ fighting in a drastically different way to their citizen counterparts. Josephus described both types of soldier as ‘hoplites’, and often it is difficult to tell them apart in his narrative – something all the more significant since he had actually fought against the Roman army. In AD 84, at the Battle of Mons Graupius against the Caledonian tribes, the Roman commander led his main attack with six auxiliary cohorts recruited from the Rhineland:
. . . to bring things to the sword’s
point and to hand-to-hand fighting; a manoeuvre familiar to them from long service and embarrassing to the enemy, whose shields were small and swords too long; . . . Accordingly when the Batavi began to exchange blows hand to hand, to strike with the bosses of their shields, to stab in the face, and, after cutting down the enemy on the level, to push their line uphill . . . in their haste to snatch victory they left many behind them only half killed, or even unhurt.
To most opponents, legionary and auxiliary infantry were much alike as aggressive formed troops, well protected by armour, possessing a short-range missile capability and very dangerous at close quarters. Both types of soldier were well trained and highly disciplined.9
The auxilia provided the army with numerous good cavalry, useful missile troops and a strong supplement to legionary numbers, producing a well-balanced, flexible fighting force. There was no permanent command structure for auxiliary units above the level of the individual cavalry ala or infantry cohort, a tenth the size of a legion. This meant that the clear hierarchy of a legion made this an important division in any substantial field force. Roman doctrine emphasised the use of reserves in battle, and armies usually formed up in at least two, and more often three or more lines of units. Cavalry deployed on the flanks, sometimes with additional units in reserve, and the infantry in the centre. Auxiliary infantry were either placed on the flanks of the legions linking them to the cavalry, or made up the first line. Tacitus praised his father-in-law Agricola for winning at Mons Graupius in AD 84 without the loss of any legionaries, but a reluctance to suffer citizen casualties was less important than the ease of keeping a legion under control until it needed to be committed to the fight. The aim was to be able to reinforce success or plug a gap if one developed, putting pressure on the enemy until they collapsed. Then the cavalry – ideally auxiliary horsemen who were still fresh – were launched in a controlled pursuit to turn retreat into rout.10
The Roman army was a sophisticated force, its different elements designed to support each other and accustomed to adapting to deal with local conditions. It was very good at fighting battles and also at capturing fortified positions, where its engineering skill and use of a range of siege engines gave it a great advantage. Light bolt-shooting catapults were sometimes used in open battle, but these and heavier pieces were even more valuable in sieges. Fortress walls were breached by battering ram, undermined, or escaladed by ladder and mobile siege tower, allowing direct assault by Roman infantry. Underlying all of this was the organised supply system allowing a force to remain in the field or encamped around a fortified place as long as was necessary. The Roman army was a force best suited to direct confrontation with the enemy’s main strength – whether this was a field army or a stronghold – which meant that strategy and tactics at all levels were aggressive, pushing for a decisive result as soon as possible. This aggression was combined with a willingness to learn from mistakes and a stubborn determination to continue a struggle until victory was achieved. The combination proved very effective, and during the first and second centuries AD the Romans won the great majority of battles they fought and rarely lost a war.
Legionaries and auxiliaries were long-service professionals. Most were volunteers, although conscription was employed at times, perhaps especially to raise auxiliaries from allied tribes. For twenty-five years soldiers were subject to strict military discipline, and when not on active service underwent training as individuals and units for their wartime role. ‘As though they had been born with weapons in their hand, they never have a truce from training, never wait for emergencies to arise. Moreover their peace manoeuvres are no less strenuous than veritable warfare. . . . Indeed it would not be wrong to describe their manoeuvres as bloodless combats and their combats as sanguinary manoeuvres.’ That at least was the theory, but Josephus’ account was too simplistic, and we have already seen that conflicting demands on soldiers’ time and their employment as builders, administrators or policemen took them away from their parent units, reducing the latter’s military readiness. The Roman army was not perfect, nor permanently kept at the highest state of preparedness for full-scale war, but even when other demands on its personnel left units weak, and lethargy and neglect undermined training, it only required effort and some little time to restore its efficiency. If the ideal condition of units could rarely be maintained for long, the average level of readiness remained high, supported by regulation and close imperial scrutiny.11
The army was probably the most heavily bureaucratic institution in the Roman world, in part because it was by far the greatest expense in the budget of the empire, and also because maintaining close control of it was important for every emperor. Record-keeping followed a soldier throughout his career. Thus on 24 February AD 103, the cornicularius or clerk of an auxiliary cohort made a copy of a document listing six new recruits, including ‘C. Longinus Priscus, 22, scar on left eyebrow’, and ‘Caius Julius Maximus, 25, no distinguishing marks’.12 Animals, especially cavalry mounts, were similarly entered in the books:
Marius Maximus to Valentinus
Received 16 March, AD 208
Enter in the records according to the regular procedure a horse, four years old, reddish, masked, without brands, approved by me; assign it to Julius Bassus, trooper of cohors XX Palmyrenorum under your command, at 125 denarii . . .13
Pay, promotions, postings and detached duties were all documented, up until the end of service. Thus we have discharges made early on medical grounds, such as ‘Tryphon son of Dionysius, a weaver of the metropolis of Oxyrhynchus, suffering from cataract and impaired vision’. In unit rosters the Greek letter theta was used as shorthand for thanatos or ‘death’, equivalent to the DD or ‘discharged dead’ in the Royal Navy of Nelson’s day, and in turn spawned the Latin slang word thetatus.14
Records were kept at unit level, while copies of some and summaries of others went to the administrative staff of the provincial legate. Inspecting the army and its bases in his province was an important part of his duties. Arrian, the Nicomedian-born Roman senator, served as legate of Cappadocia under Hadrian, and left an account of a tour of the garrisons on the eastern coast of the Black Sea. His Periplus was a literary essay, written in Greek, and twice mentions the fuller and more formal Latin report, which sadly does not survive. Even so it gives a sense of his activities: ‘before midday we came to Apsaros, where five cohorts are stationed. I gave the army its pay and inspected its weapons, the walls, the trench, the sick, and the food supplies that were there’. At Phasis,
. . . the fort itself, in which 400 select troops are quartered, seemed to me, owing to the nature of its site, to be very secure, and to lie on the most convenient spot for the safety of those who sail this way. In addition, a double ditch as broad as the other. The wall used to be of earth, and wooden towers were set above it, now both it and the towers are made of baked brick. And its foundations are firm, and war engines are installed – and in short it is fully equipped to prevent any of the barbarians from even approaching it, let alone to protect its garrison there against the danger of a siege.
Like Pliny, Arrian looked to make further improvements, and in this case ordered a new ditch to be dug surrounding the civilian settlement outside the fort and protecting the harbour. Twice he mentions issuing pay to the garrisons – due three times a year – and talks about inspecting men, equipment and horses, as well as visiting the hospitals. There are few details of the exercises troops were required to perform. Arrian mentions getting a small detachment of cavalrymen to throw javelins, and another unit of horsemen to demonstrate leaping onto their horses – an important skill since the stirrup had not yet been invented.15
Some sense of the type of drills and exercises performed on such occasions comes from a long inscription from the base of Legio III Augusta at Lambaesis in Numidia. It records the speeches made by Hadrian after personally watching the army of the province going through its paces during his visit. His verdict was highly favourable – hence the desire to commemora
te it – and in many ways his comments could have been made by a senior officer in many armies over the ages. Hadrian displays a close knowledge of the local situation, telling the III Augusta that he was aware that they were under-strength. He knew that:
. . . a cohort is away because, taking turns, one is sent every year to the staff of the Proconsul [of Africa]; that two years ago you gave a cohort and five men from each centuria to the fellow third legion, that many far-flung outposts keep you scattered, that twice within our memory you have not only changed fortresses but built new ones.
All of this would have excused some deficiencies in their performance, but no such excuses were necessary and he praised the legion, its officers and the care of the legate. During the exercise the legion deployed in battle order, marched, built a marching camp with stronger defences than was common, cared for its weapons and cooked meals as if on campaign. Auxiliary units were put through their paces in a similar way. Hadrian watched infantry archers shooting and cavalry manoeuvring, jumping obstacles and throwing javelins. There were constant admonitions on the value of rigorous training, salted with occasional, detailed criticism where he felt this was necessary. The men of a cavalry ala were warned against attacking or pursuing too boldly, for ‘nothing must ever be done recklessly’. Hadrian felt that the cavalry of III Augusta had made some of the drills too difficult in the hope of impressing him, but praised their spirit. The Ala I Pannoniorum particularly impressed him. ‘Had anything been lacking, I would note it; had anything stood out, I would mention it. You pleased throughout the whole manoeuvre.’16
No doubt an imperial visit encouraged a provincial army to put on as impressive a show as possible, especially if, like Hadrian, the princeps was well known for his deep interest in drills, skill at arms and equipment. There would be plenty of warning and time to prepare – just as the emperor was no doubt carefully briefed on the local situation so that he could demonstrate his concern for and knowledge of his soldiers. Exercises staged for the provincial legate would most likely be on a smaller scale, although still focused on essentially the same things – the javelin-throwing and vaulting into the saddle mentioned by Arrian find parallels in Hadrian’s speeches at Lambaesis. We do not know how often a legate was expected to review the units under his command, whether this was just done on arrival in the province or was an annual event. Arrian’s testimony suggests that written reports would be sent to the princeps giving a verdict on the state of each unit and their commanders – something likely to influence the latter’s careers.17
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