`Shall I now proceed to recall, as though they were something new or previously unheard of, the reconquest, by your valour, of the Gallic province, the subjection of the whole barbarian race, when these triumphs have, in this part of the Roman Empire, been hailed as most deserving of glory by the laudatory voice of popular acclaim, to such an extent as to merit the envy of your cousin the Emperor?' - Speech of thanks to Emperor Julian by Claudius Mamertinus, delivered z January 362.'

For all the magnificent ceremonial of the imperial court, no emperor was ever free from the fear of usurpation. It was a very personal and immediate threat, for challengers obviously did not want to destroy the empire, simply to possess it. Being killed by a rival remained the most frequent cause of death for emperors. Successful usurpers needed the support of a substantial section of the army. Emperors could try to monitor the loyalty of senior officers, giving important commands only to the most loyal. They also continued to make soldiers take an oath of personal allegiance, and to remind them of their loyalty with parades and donatives on significant imperial festivals throughout the year. Yet, inevitably, they remained distant figures to the overwhelming majority of their troops and most of their officers.

The risk that his army might turn against him was something an emperor had to live with. Emperors could not dispense with the army, or even reduce its size substantially and so hope to reduce its power. In the first place, any serious reduction would have created large numbers of unemployed officers as well as demobilised troops. At the least this was likely to increase banditry within the provinces - when Septimius Severus had dismissed the praetorians there was a rapid increase in levels of armed robbery in Italy. More probably it would have created an immediate power base for a usurper who promised to reinstate them.'

Yet the main reason the army could not be reduced was simply because it was necessary. None of Rome's foreign enemies threatened its existence. The tribal peoples were disunited - mostly they raided, and at the very worst might nibble away and occupy small areas of land in the frontier zones. The Persians were both more united and more sophisticated militarily, but even they could not hope to do more than win back some of the territory lost to the Romans. Foreign wars were not life and death struggles, at least as far as the Romans were concerned, but they were frequent. Rome had many enemies living alongside its vast frontiers. Just because none of them individually posed an overwhelming threat to the empire did not mean that they posed no threat at all. Violent crime does not threaten the existence of modern democracies, but in turn that does not mean that it can simply be ignored, even if governments and voters seem resigned to its frequency in some areas. For the Romans, raiding across the frontiers needed to be kept at a level the government could accept. Warfare also played a central role in imperial ideology. Winning victories over foreign opponents was the ultimate proof of an emperor's capacity to rule, any success receiving a prominent place in their propaganda. The desire for glory certainly inspired successive emperors to launch frontier campaigns.

A `New Model'Army

As we have seen, Diocletian and Constantine presided over a major restructuring of the army, alongside their reform of civil administration. Troops were now divided into two distinct grades, the comitatenses and limitanei. The latter received less pay and had lower physical requirements, but were still full-time professional soldiers. The root of the name was the word for military road (limes), although there is some dispute as to the precise significance of this. The limitanei were also sometimes called riparienses, which came from ripa (the banks of a river). They were stationed in provinces, usually in frontier areas, and were commanded by duces. Their role was to patrol and police the area around their garrisons and deal with relatively small-scale attacks, such as raiding bands numbering a few dozen or at most a couple of hundred warriors. One study has noted that we never hear of raiding bands of less than 400 men and suggested that smaller groups were routinely stopped by the limitanei.3

The comitatenses had an entirely separate command structure and were more likely to be moved from one region to another. The name was derived from comitatus (the imperial household), and the original idea was clearly that they should be at the emperor's disposal. It is possible that under Constantine they were organised as a single army, ready to follow on campaign wherever he went. When his three sons divided up the empire in 337, the comitatenses were divided into three separate armies. Over time, more distinct armies stationed in specific regions would be created. In practice, the comitatenses were usually commanded by generals with the title `Master of Soldiers' (MagisterMilitum), such as Silvanus and Ursicinus. Variants of the title included `Master of Horse' (Magister Equitum) and `Master of Infantry' (Magister Peditum), neither of which commanded exclusively infantry or cavalry, but a mixture of both. As subordinates, the Masters of Soldiers had officers with the rank of comes (count, pl. comites). Again, the word had its root in the personal companions who had traditionally accompanied an emperor on a journey or campaign. In some cases counts were given small-scale independent commands.4

The Masters of Soldiers regularly commanded substantial numbers of troops, although it is unlikely that these forces were bigger than the army controlled by a senatorial legate in a major military province in the first or second century. There were only three of them - the number would double by the end of the century, but never increase beyond that - and this made it easier for the emperor to keep a close watch on them. Yet the Silvanus episode had shown that this might not be enough. More important in ensuring the emperor's security were the complex divisions of responsibility and power throughout the provinces. The army was divided into two, with comfortably over half of its units being limitanei. However, co-operation between limitanei and cornitatenses does appear to have been common, and senior officers could in practice find themselves with troops of both types under their command during a campaign. A much bigger division was maintained between the army hierarchy and the civil administration.

The army depended on the civilian bureaucracies to supply it with pay, food and clothing. Even weapons and other equipment, which in the early empire had been made in the legions' own massive workshops, were now provided by state-run arms factories under the supervision of the praetorian prefects. A Master of Soldiers planning to challenge the emperor had to secure not just the support of his soldiers, but the cooperation or replacement of large numbers of bureaucrats. It was much harder for one man to know, and win over, everyone who was important. At the same time, there were many people serving in independent hierarchies able to send real or fabricated reports of the disloyal behaviour of others. The system offered some protection to the emperor, at the cost of making it more difficult to get things done. Campaigns could be delayed or hindered by lack of supplies over which the commanders had no control.'

The Roman army in the fourth century was large, its manpower still dwarfing that of the swollen bureaucracy. The vast majority of the men paid and under the control of the emperors were soldiers. Yet we do not know how big the army was. Most scholars assume that it was larger than the second-century army, perhaps 50 per cent or even ioo per cent bigger, but the evidence is inadequate and inevitably the calculations involve a good deal of conjecture. We do know that the fourth-century army contained many more units and we have a complete list of those in existence at the very end of the fourth and the beginning of the fifth century. Some units had disappeared since Constantius II's time, others had been created, but this list gives us a fair idea of the overall shape of the army in his day. Unfortunately, we have no certain evidence for the size of each unit so cannot calculate the army's theoretical total size from this.6

The limitanei included a very broad range of unit types. Some were survivals from the time of Marcus Aurelius and even earlier. There were legions, as well as auxiliary cohorts and cavalry alae. Others were new creations. Overall, there was a higher proportion of cavalry units in the limitanei than in the comitatenses, no doubt because they were useful for patrolling. There were no units including both infantry and cavalry, equivalent to the mixed cohorts of the early empire. Legions were sometimes stationed in several outposts. Several were split amongst five garrisons, while in the early fifth century the Legio XIII Gemina provided five garrisons on the Danube, another in Egypt and also had a unit amongst the comitatenses. Even so, they were certainly far smaller than the 5,ooo-man legions of the early empire. It is also more than possible that most units were smaller than the roughly Soo-man cohorts and alae of the auxiliaries in the second century. Very many of the forts occupied by the limitanei were tiny, most a small fraction of the size of earlier auxiliary forts. An Egyptian papryus dating to the start of 30o also suggests some very small units. It mentions a cavalry ala with ii6 - just over a year later this had risen to ii8 - a vexillatio of legionary cavalry with 77 men and a unit of mounted archers with 121. A number of units of legionary infantry averaged around the 500 mark, but a camel troop seems to have had just a couple of dozen men.7

The situation with the cornitatenses is no clearer, although there was less variety of unit types. Infantry consisted of legions and a new type of unit known as auxilia. All of the latter and some of the former were rated as palatina, a title that carried much prestige and some tangible advantages in pay and bonuses, but no difference in function. Cavalry units were all called vexillationes and were smaller than the infantry regiments. A common estimate is to give cavalry units a strength of boo and the infantry somewhere between I,ooo and 1,200. However, the few mentions of regimental strengths in our sources suggest smaller numbers, averaging around 350-40o and Boo respectively. What we do not know is whether such lower figures represent actual campaign strengths, reduced by disease and casualties, or theoretical sizes. A couple of sources mention commanders who kept non-existent men on their unit's role so that they could draw their pay and rations. Infantry units of colnitatenses were brigaded in pairs, and seem to have permanently operated together. This obviously adds an extra complication since we cannot be sure whether numbers in our sources refer to a single regiment or a pair that the author naturally assumed would be together!

Overall, it is fair to say that the units of the fourth-century army were smaller than their first- and second-century predecessors. Going much further than this quickly becomes conjectural. We cannot even be sure that all units of a particular type had the same theoretical size. Infantry regiments of all types in the field army were probably somewhere between 500 and i,ooo men strong, cavalry units about half the size of infantry. Many units of limitanei may have been a good deal smaller, and perhaps we should think in terms of 50 to 200 men, which would make them more like companies than battalions by modern standards. It is possible that on paper the total strength of the army was larger than in Marcus Aurelius' day, but we cannot be sure of this. Its actual strength on a dayto-day basis is even harder to assess.'

The evidence is equally poor for the army's recruitment. Some men were volunteers and others conscripts, but the balance between the two is unknown. Sons of soldiers were legally obliged to join the army. Landowners had to supply a set number of recruits as part of the taxation system, but were often able to commute this duty to a money payment or avoid it altogether. There was also a steady supply of drafts for the army from the groups of barbarians settled by treaty within the empire and obliged to provide soldiers for the army. Tribesmen from outside the empire also came as individuals or as groups to enlist in the army. The old idea that this influx of Germans `barbarised' the Roman army and over time reduced its efficiency has been discredited. There seems to have been no real difference in reliability and performance between recruits from inside or outside the empire. As we have seen in the last chapter, the senior ranks included many men of barbarian descent who behaved exactly like colleagues of more traditionally Roman stock.

The army took recruits wherever it could get them, and there are clear signs that many people went to drastic lengths to avoid service. In real terms army pay was of less value than it had been in the first and second centuries, while discipline and punishment remained brutal. Repeated laws punished the practice of self-mutilation to avoid being conscripted - potential recruits cut off their thumbs so that they would be unable to hold a sword or shield properly. There was a famous case of an equestrian who had done this to his sons during Augustus' reign, so the practice was not new, but it does seem to have become more common. The frequency of legislation dealing with the problem suggests that the laws were not effective. A letter from a clergyman to a garrison commander in Egypt asked that he exempt a widow's son from conscription or, failing that, at least enlist him in the local limitanei so that he could stay near home instead of sending him away to join the comitatenses. The fourthcentury army did not have massive resources of manpower and this factor played a significant part in shaping its operations.'°

Whatever the actual size of the fourth-century army, more units certainly meant more officers to command them. Regimental commanders were usually called tribunes, although other titles such as praepositus were also used. Such a post gave a man considerable status - even if, once again, his pay and social importance were somewhat less than those of an equestrian officer in the second century. In comparison to the early Principate, the Late Roman army was top heavy in its command structure. It is more than likely that the desire to reward supporters with high rank - and in some cases their own independent commands - had as much to do with the multiplication of units as any practical concerns. We hear of unattached tribunes, sometimes serving in a staff capacity, and it is more than likely that there were significantly more men with commissions than there were units for them to command. Some tribunes may well have been promoted after service in the ranks. A much more common route was to be commissioned from special units at the imperial court. The candidati (candidates) acted as personal bodyguards of the emperor during court ceremony. The protectores domesticiserved as junior staff officers either with the emperor or a Master of Soldiers. Ammianus was one of these. Promotion was officially the emperors' prerogative, but in practice he had to rely on recommendations of senior officers, officials and courtiers. There was no formal system for training these officers or for selecting on the basis of talent. As always in Roman society, patronage played an important role in determining a man's career."

Modern scholars conventionally refer to the comitatenses as mobile field armies, and often they go further and dub them elite troops. They are seen as a necessary response to the greater external threats facing the empire. In the past, wars requiring the removal of troops from one frontier zone weakened defences there and left the region vulnerable to attack. In the fourth century the limitanei remained permanently in place. They were not as numerous as the forces on the frontiers in the early empire and could not hope to defeat major incursions. Yet their bases were strongly fortified, as were towns and cities, and they were expected to hold out for as long as they could and harass the enemy. A sizeable army of comitatenses could then be sent to the region to confront the invader. In essence, they formed the mobile reserves that it is claimed the earlier deployment lacked."

Much of this analysis has been called into question, particularly the sense in which they acted as reserves. Nothing of this sort is ever implied by the ancient sources. No army could ever move faster than an infantryman could march, and more often than not its speed was reduced to that of the plodding draught oxen that pulled its baggage train and carried its food supply. Given the size of the empire, talk of reserves makes little sense, since unless they were fairly close to the theatre of operations then it would take them a very long time to get there. In spite of such criticism, the `mobile field army' tag has stuck, so that it is worth making a few points about the actual deployment and use of the cornitatenses.

Unlike the lilnitanei, the colnitatenses did not occupy permanent garrison posts. When not on campaign they were stationed within the provinces and not on the frontiers. However, they were not kept concentrated as large army corps ready to take the field at a moment's notice, since this would have made it difficult to supply them. Temporary camps, the men living in tents or roughly built shacks, were unhealthy in winter, and in any case it was dangerous politically to keep armies concentrated during the winter months of inactivity in case they rebelled. The army did not build large bases in this period, and even many of the existing legionary fortresses designed to accommodate 5,ooo men in the second century were now abandoned or substantially run down. At the beginning of the sixth century the historian Zosimus claimed that Diocletian had kept the empire secure by stationing the whole army along the frontiers in strongly fortified posts. `Constantine abolished this security by removing the greater part of the soldiery from the frontiers to cities that needed no auxiliary forces.' Once there, he claimed that the soldiers became a burden on the communities and were themselves softened by the pleasures of urban life."

When not on campaign - and even at the most intensive periods of operations these were rarely conducted over winter - the comitatenses were dispersed in towns and cities within the provinces. It is doubtful that more than a brigaded pair of units were often stationed in one place. This spread the burden of feeding them and made it harder for the units to join together and back a usurper. In addition, it provided trained soldiers to man the city walls in the case of a sudden threat from a foreign enemy or a rival for imperial power. There was nothing especially new about stationing troops in or near towns. This had been common in the eastern provinces in the first and second centuries, although there was a well-established literary cliche that maintained it had an enervating effect on them.14

Yet in the earlier centuries army units had normally lived in their own barracks within or near to cities. This does not seem to have been the case with the cornitatenses - although admittedly the archaeological evidence for the layout of most towns in the fourth century is extremely limited. Instead, they were billeted in civilian houses, and legal documents talk of officials painting on the door posts the number of men and the unit from which they should come. Throughout history billeting has frequently caused friction between soldiers and civilians. From a military point of view, the dispersal of units in small groups over many separate dwellings was not conducive to good discipline. In their purposebuilt barracks the units of the first- and second-century army had been concentrated in one place under the close eye of their officers. They were provided with good sanitation, exercise and bathing facilities, as well as hospitals for their sole use, and had parade grounds and training areas readily available. Facilities in cities and towns were far more limited and not for the exclusive use of the military. Even the largest city might well struggle to find good stabling for the 500-1,000 horses mustered by a couple of cavalry regiments.

Distributing the comitatenses in cities was the easiest solution for the government, but was scarcely the best way to keep them in good con dition. Military training was and is not a simple thing, permanently instilled once it is learned, but something that must be constantly repeated. As important was physical fitness - essential for the marches required on campaign, let alone actual combat. Both were harder to maintain when the army was split and billeted in civilian settlements. There was also inevitably a delay in concentrating the units before a campaign could be begun. The army may have maintained some pack and baggage animals permanently - and if so these were an extra burden to the communities on top of the cavalry mounts - but still needed to requisition or purchase many more to carry its food and other stores in the field. All this took time and faced the added complication of much of it being controlled by bureaucracies entirely separate from and with different priorities to the army.

It is reasonable enough to call the comitatenses field armies. They were more mobile and should usually have been more effective fighting units than the limitanei, at least for large-scale operations. Yet, on the whole, there was nothing particularly innovative about them, certainly nothing that would justify calling them elite. The physical requirements were the same as for service in the earlier army, and later in the century even these would be reduced. Over the course of time, some units of limitanei were attached permanently to the field forces, receiving the halfway status of pseudocomitatenses. This suggests that there was no stark distinction in the military potential of the two grades of troops. In the end, troops were as effective as their training, leadership, tactics and equipment allowed. Only the Persians came close to matching the army tactically, and barbarian armies were markedly inferior. The factory-produced equipment of the fourth-century army has a more functional look than the armour and weapons of the early empire. Both the pilum (heavy javelin) and short gladius (sword) had fallen out of use. Instead, the standard weapons were a long-bladed spatha (sword) - previously only used by cavalrymen - and simpler spears suitable for both thrusting and throwing. As an individual, the Roman soldier was still a well-equipped fighting man. Infantry tactics were probably a little less aggressive, but remained effective. The fourth-century army won the great majority of the battles it fought.15

The standards of training and quality of leadership of the fourthcentury Roman army inevitably varied - as indeed they had done in earlier periods. On average standards may have been a little lower, but it remained the only professional army in the known world. The demise of the 5,ooo-man legion removed one command level useful for operating and controlling very large armies in the field. It also meant that it was harder to support large numbers of specialists - engineers, architects, siege specialists, artillerymen etc. - within the army and pass on their experience to successive generations. The comitatenses had no permanent bases to act as depots and to maintain records of personnel, their postings, equipment and mounts. Records were still kept, but had to be moved continually if they were to remain useful to the unit. The same was true of soldiers. New recruits, convalescents or detached men returning to normal duty would have to travel to rejoin the parent regiment wherever it happened to be. The frequency with which a unit went on campaign would have steadily worn it down. Some men would be lost to enemy action, many more to sickness or detachment. This meant that large numbers of men may have existed and been rightfully paid by the state, but would not actually be present with their unit when it went on campaign. The probability that most units were heavily under strength most of the time makes it all the harder to estimate their full theoretical complement."

We should not exaggerate the efficiency of the fourth-century Roman army, but neither should we forget just how unique it was in its day. For all the complexity of arranging supplies, the Romans did possess a system for organising these things on a massive scale. The fourth-century army was far from perfect, but still enjoyed marked advantages over all its opponents. We need always to remember that it had been shaped by almost a century spent fighting itself. Diocletian and Constantine did not create an army according to a coldly logical design, changing the military system of the second century because it was obsolete. Instead, they patched together a unified force from the badly dislocated debris left by generations of civil wars. Their first priority was always to protect themselves from challengers, and every other consideration was secondary to this. The immediate threat of civil war never went away and continued to dominate the thoughts of their successors. Given this context, the fourth-century army was highly effective, and it is worth now looking at it in action.

A New Caesar in Gaul

Constantius II was understandably concerned that Gaul had produced a second usurper so soon after the suppression of Magnentius. In the end, he decided that a family connection was the strongest basis for trust and summoned Gallus' half-brother Julian to Milan. On 6 November 355 the twenty-four-year-old was proclaimed as Caesar at a massed parade of the troops. Ammianus notes that the soldiers showed their approval by banging their shields against their knees. If they were displeased, then they lifted the shields off the ground and clashed the shafts of their spears against them. Just like his brother before him, Julian had received no preparation for high office. Unlike his brother, he not only left a considerable body of writings that have survived to this day, but also generally receives much more favourable treatment in our sources, at least for this stage of his life.'

The army in Gaul had shown a willingness to rebel against the emperor, but strong forces had to be kept there to protect the provinces from attacks from the tribes across the frontiers. Along the northern stretches of the Rhine were the Franks, and to the south in the lands between the Rhine and Danube were the Alamanni. These were the two main groupings, but other peoples also launched periodic attacks. Neither the Franks nor the Alamanni were unified nations, but a large number of separate groupings of tribes and clans under chieftains whose power rose and fell over the course of time. Some of these smaller groupings would sometimes accept common leadership, but this was never universal. Their attacks on the empire were almost without exception raids aimed at plunder and not occupation. There were no hordes of barbarians hurling themselves time and again against the walls of civilisation. The population of the area occupied by the Alamanni was probably less dense than in the nearest sections of the Roman provinces. Raids on their own would not destroy the empire, but they did make life extremely unpleasant for those caught up in them. We hear of many captives taken back to lives of slavery beyond the frontier. Isolated settlements were destroyed and even some substantial towns overrun and plundered. Having a circuit of walls was not always much protection if they were not maintained or if there was no one organised enough to defend them. Julian later claimed that no fewer than forty-five major towns had been overrun before he arrived in Gaul."

Civil war encouraged barbarian attacks, in the pattern we have already seen in the third century. Internal struggles took Roman troops away to slaughter each other, leaving the frontiers vulnerable. They also tended to dislocate trade with the tribes outside the empire, making some communities desperate enough to resort to warfare. The Alamanni seem to have provided the Romans with timber and building stone in peacetime. Roman leaders were also ever willing to enlist barbarian allies to fight against their rivals. Magnentius hired large numbers of warriors from outside the empire. Constantius doubtless did the same, and also encouraged the Alamannic king Vadomarius to invade the usurpers' territory, granting him the right to settle on the west bank of the Rhine, taking part of the Roman province. Such pragmatic deals were attractive during civil war, but became somewhat embarrassing afterwards. As usual, victors in civil wars were very eager to win some clean glory by defeating Rome's foreign enemies. It was not always easy for tribal leaders to keep up with the dramatic switches of attitude from their Roman allies. Civil wars and raids also created human flotsam - deserters, the dispossessed, runaway slaves and fugitives - and such desperate men joined raiding bands or became bandits in their own right. It must often have been difficult to know the identity of plunderers."

Julian read Julius Caesar's Commentaries on the Gallic Wars as he travelled north to take up his new command. The world had changed a lot in the last four hundred years, but the new Caesar soon showed that he could match the famous general's driving ambition. He embraced the military life with enthusiasm. The tradition favourable to him claims that he was hindered by senior officials and subordinates sent by Constantius to keep a close watch on him. This is clearly an exaggeration, and he probably needed a good deal of advice and guidance as he set about his task. Ursicinus initially remained in post as Master of Soldiers to act in this guiding role. However, as a clever man who had spent most of his life alone with his thoughts, Julian was reluctant to accept opinions other than his own."

In 356 Constantius himself led a major operation against some of the Alamanni, which Julian and his troops supported. (A casual reading of Ammianus gives the impression that things were the other way around, with the Caesar playing the dominant role.) Julian led the northern column, while the Augustus commanded a larger army in the south. It was essentially a demonstration of force, intended to show the tribes that the Romans were once more united and ready to deliver a massive attack on anyone who displeased them. The aim was to negotiate new treaties with the tribal leaders from a position of overwhelming Roman dominance. There was little actual fighting, although Julian won a few skirmishes. The initial encounters occurred before he joined the main force - an indication of the time taken to muster a field army - and while he was accompanied only by a unit of cataphracts and another of ballistarii (which literally means `artillerymen', but in this case they were probably equipped as infantry, just possibly with a form of crossbow). Even with his bodyguard he may not have had many more than a thousand men, but this was easily enough to brush aside the raiding parties he encountered.2'

The main force was concentrating at Rheims, and en route Julian liberated Autun, Auxerre and Troyes. There were no enemies in any of these towns. Autun had recently been attacked, but the raiders had been repulsed not by the troops in garrison, but by a scratch force of retired soldiers who had banded together to act. At Troyes the gates were barred to him for some time, until he was able to convince those in charge that he was actually a Caesar and the legitimate representative of Roman power. This rather suggests it was sometimes difficult to tell the difference between formed units of the Roman army and a marauding band. Combining with the rest of his army, Julian proceeded to pass through more towns, marching along the Rhine until he reached Cologne. This had fallen to the Franks some time before, but they do not seem to have stayed very long. Again, the campaign was essentially a demonstration of force, showing the government's power to communities who may well have felt abandoned in recent years.

Julian spent the winter in Senon (perhaps modern Sens, but more probably near Verdun) and was blockaded by a band of Alamanni. He did not have many troops with him - as usual, logistic concerns meant the army had dispersed into winter quarters - and so was unable to drive them off. In the end, failing to provoke a surrender, the warriors just sloped off quietly. Julian blamed Ursicinus' successor Marcellus for failing to come to his rescue. Constantius recalled him, refusing to accept his evidently justified explanation that there had never been any serious danger to the Caesar."

In 357 a similar campaign was planned, but Constantius did not take part and left the main force under the command of the new Master of Soldiers Barbatio. The latter had 25,000 men to Julian's 13,000, but the two men failed to co-operate. There may have been a number of reasons for this, including mutual suspicion, but it did not help that Barbatio seems to have had at best modest talent. He suffered a serious reverse and retreated, losing his baggage, leaving Julian to press on alone, launching several raids against tribal settlements. Outside Argentorate (Strasbourg) he encountered a strong army of Alamanni, led by seven kings. Two of these - Chnodomarius and his nephew Serapio - were in command. There were also ten more lesser kings and many noblemen with the army, each with their band of followers, as well as some mercenaries. Ammianus claims that the whole army numbered some 35,000, but this is more than likely an exaggeration. Perhaps the Alamanni outnumbered the Romans. They were certainly confident - some years earlier Chnodomarius had defeated Magnentius' brother. The leaders were willing to fight, but they may have hoped that a display of force would make the Romans negotiate for peace.

Julian did not answer their ambassadors. His army had marched some distance and his initial plan was to fortify a camp, rest his soldiers and fight on the next day. He was persuaded to attack by his senior officials, including his praetorian prefect. They saw this as a great opportunity to defeat so many leaders in one place and claimed that the soldiers would deeply resent being held back. Julius Caesar emphasised that he never gave in to pressure from his men and fought only at times and places of his own choosing, but conditions in the fourth century were different. Julian let himself be persuaded. The Romans advanced and battle developed into a hard slogging match. Julian's cavalry broke and fled - one unit was later made to parade in women's clothes as a punishment. He rallied them, and when a group of warriors led by the chieftains broke through the first line of Roman infantry, they were stopped by reserves. In the end the Romans' discipline and clear command structure prevailed and the Alamanni were routed. Roman losses were 243 men and four tribunes. The Alamanni lost far more, as beaten armies nearly always did in the ancient world, although Ammianus' figure of 6,ooo dead is probably another exaggeration.14

Strasbourg was a significant victory, but it was also the only pitched battle Julian fought in five years of heavy campaigning in Gaul. More typical was what followed, with a series of savage raids being launched against the tribes. The Roman army won most of the battles it fought during the fourth century, but battles were always risky. A defeat was likely to involve heavy casualties, which it would be hard to replace. Surprise attacks allowed the enemy to be terrified into submission at little risk to Roman lives. Even if a raid was spotted by the barbarians, they were rarely able to gather enough warriors to meet it in time. The worst that was likely to happen was that the raiders would fail to catch anyone. To support the raids a number of abandoned Roman forts were reoccupied, giving the tribes the impression that they were under constant surveillance. This was deeply resented."

The scale of operations is well illustrated by an episode that occurred in the winter of 357-358, when Julian spent a couple of months besieging a band of Franks who had holed up in two abandoned forts. There were only boo warriors, and he probably kept no more than a couple of thousand soldiers with him to mount the blockade. More would have been unnecessary and very hard to feed in winter. When the Franks finally surrendered they were sent to Constantius as recruits for the army. The episode is striking because the Romans were reluctant to assault such a small force of barbarians. They did not want casualties on either side since the enemy were themselves a useful source of manpower. Even more remarkable is the simple fact that the Caesar himself was willing to devote many weeks to supervising such a small scale operation.26

During his time in Gaul, Julian aggressively reasserted Roman dominance along the frontier. In some cases he seems to have turned on communities that had not long past been allied with Rome. Julian wanted and achieved military glory. He needed to be popular with the army and with provincials if he was to avoid the fate of his older brother. He considerably reduced the tax burden on the communities in Gaul in spite of bitter opposition from his praetorian prefect. The scale of the reduction showed the level of graft amongst the officials collecting the levies, but it was a dangerously populist gesture. Constantius had murdered Julian's father and many of his relatives, and more recently executed his brother. It was very hard for either man to trust the other fully.27

In 36o Constantius ordered Julian to send four regiments of auxilia palatina and 300 men from his other units (whether individual regiments or brigaded pairs is unclear) to reinforce the army in the east. The Persians had launched a major offensive in the previous year so that the need for men was genuine. On the other hand, he had begun the process of removing Gallus by stripping him of his forces. The proposed move was also unpopular with the soldiers in Gaul, many of whom were local or from across the frontiers. Some were supposed to have been promised that they would never serve south of the Alps, let alone further afield. In February 361 Julian was proclaimed Augustus by the troops with him at Lutetia (modern Paris). He feigned reluctance in the traditional way, but soon agreed `and lifted onto an infantryman's shield, he was raised up, saluted as Augustus, and asked to put on an imperial diadem. When he denied that he had one, they urged him to use a necklace or headband of his wife's.' Julian felt that this would be a bad omen, and similarly disliked the idea of using something from a horse's decorative harness, but finally agreed to wear a neck torque donated by one of the standard bearers.z8

Ammianus' claim that Julian was genuinely reluctant and pressured by a spontaneous outburst from the soldiers is unconvincing. More probably, the issue of the postings to the east was a convenient moment to implement long-nurtured plans. One comes known to be loyal to Constantius had recently been despatched to Britain. On his return he was immediately arrested before he could learn of Julian's elevation. The new Augustus wrote to Constantius, repeating the story of his reluctance and hoping for reconciliation, but he refused to accept the demand that he return to the rank of Caesar. In the summer Julian took his army - presumably including the men who had previously resisted going east - and advanced to confront Constantius. The balance of forces favoured the latter, but in the autumn he fell ill as he crossed Asia Minor on his way back to confront the usurper. Constantius II died on 3 November 361 at the age of forty-four. His only son was an infant and there were no other close male relatives left apart from Julian. Therefore, there was no challenge to the rebel becoming sole emperor."

Julian was especially aggressive during his time in Gaul. He needed glory and the situation was unusually disturbed on the frontier in the aftermath of Magnentius' rebellion. By surprise attacks, which massacred or took prisoner the entire population of some villages, through broader demonstrations of force and the reoccupation of abandoned forts, the idea was to convince the neighbouring peoples of Rome's overwhelming power. Roman methods were often utterly ruthless. The preference was always for one-sided slaughter than the risk of an open battle. In To a raiding band of Saxons was overawed by the arrival of strong Roman forces and preferred negotiation to fighting. In return for giving hostages, the raiders were granted the right to return to their homeland. However, the Romans never had any intention of honouring the agreement and instead prepared an ambush. The plan nearly back-fired, when some men emerged from hiding prematurely and were cut up by the Saxons. In the end the barbarians were overwhelmed by weight of numbers and all slaughtered. Ammianus noted that while this might seem `hateful and treacherous', mature reflection showed that it was only right for the Romans to destroy `a band of robbers when they had the chance'. Most of these frontier operations were very small-scale. Julian never led his army further than 30 miles east of the River Rhine. The dominance was only intended to be local. It was also likely to be temporary, since the savagery of Roman actions and the unpredictability of their internal politics were bound to instil nervousness and hatred that would burst out in the future.3°

Alongside the threat and use of military force went active diplomacy. Some tribal aristocrats took service in the Roman army and rose to high rank. Many more were turned into allies and given financial aid. Often their sons were raised as hostages within the empire and given a suitably Roman education. One of the two main Alamannic leaders at Strasbourg was named Serapio because his father had developed a reverence for the god Serapis during his time living within the empire. Chieftains regularly dined with senior Roman garrison commanders in frontier posts, allowing both sides to study the other and guess at future events. On several occasions the Romans exploited this tradition to imprison or murder an important guest.

The tribal peoples were a minor but frequent threat to the empire. At times the Romans were able to gain such a position of dominance in a frontier region that there would be no serious operations for a generation. The Goths along the southern Danube seem to have been fairly quiet for decades after Constantine's campaigns in the region. There was usually friction somewhere along the frontiers with some of the peoples living outside, but most often it was small-scale. Serious incursions in Britain were satisfactorily dealt with by sending a comes with just two pairs of auxiliapalatina regiments from the field army in Gaul. The chief military activity of the barbarian tribes was always raiding. The Romans responded by trying to catch the raiders, usually on their way back, slowed down with their spoils. The Romans relied on fast marching and surprise attacks every bit as much as their enemies. Many of the campaigns described by Ammianus are very small-scale and the details he gives are far more intimate than the sort of thing mentioned in accounts of warfare in earlier periods. We read of raiding bandits overwhelmed when the Romans surprised them while they were bathing and dyeing their hair red in a river. Elsewhere he tells of another group massacred when the Romans deliberately broke the truce during negotiations. At one point during Julian's campaigns, Ammianus notes that: `Besides these battles, many others less worthy of mention were fought in various parts of Gaul, which it would be superfluous to describe, both because their results led to nothing worthwhile, and because it is not fitting to spin out a history with insignificant details.' This is all the more striking given the small size of most of the skirmishes he does mention. What is so different from earlier periods is the number of times he describes emperors taking personal charge of very small operations. In the first or second centuries such matters would have fallen to a senatorial governor, or often one of his subordinates. It was much harder to get things done in the fourth century.31

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