Traditionally it has been assumed that Germanic society changed in the second and third centuries, the small individual tribes coalescing to form great tribal confederations that posed a far greater threat to the security of the Empire. When these groups came under pressure from peoples migrating from further east, the Roman Empire was unable to sustain their onslaught and collapsed. The long series of wars fought by Marcus Aurelius against the Marcomanni and Quadi is supposed to have foreshadowed the emergence of powerful peoples like the Alamanni and the Franks who were to ravage Gaul in the third century. This view is at best an exaggeration. Tribal peoples had long displayed a tendency to unite under a strong, charismatic leader, but such developments rarely outlived this man. Arminius had led a confederation of tribes against Rome until he was assassinated by rival noblemen. Prior to this he had defeated Maroboduus, king of the Marcomanni, who had created a strong power base by adding subject tribes to his own people. In neither case did a similarly strong leader appear to unite these tribes for well over a century. Most of the tribal peoples of Europe seem to have existed in a continuous cycle of unification and fragmentation. It is possible that the presence of the Roman Empire did encourage the trend towards unification. The payment of subsidies and the supply of large quantities of prestige goods allowed noblemen to build up their following and strengthen their position within the tribe. Roman attacks upon a tribe may also have encouraged support for leaders who fought successfully against Rome. However, any change was one of degree and did not affect the fundamental nature of tribal society.
Most aspects of Germanic society, especially their military institutions, changed very little from the first to the fourth centuries. Even peoples such as the Alamanni, Franks and Goths were usually disunited, each geographical unit of settlements, the clan or canton, being ruled by its chief or sub-king. At some periods a single nobleman might be acknowledged as leader of several neighbouring clans. Armies continued to consist of a small permanent element, the warriors (comites) supported by each nobleman, and the mass of warriors composed of all free men able to equip themselves. It is difficult to estimate the scale of tribal armies with any precision. In 357 two Alamannic kings who were supported by other sub-kings and chieftains are credited with a force of thirty- five thousand men composed of their own war bands, warriors from their cantons and some mercenaries from outside the tribe. It is doubtful whether Germanic armies were ever able to muster more men than this in one place, and even this size was exceptionally uncommon. We are told that one of the two leaders of this army had two hundred warriors in his immediate following or comitatus, but this was probably unusually large.
The most common threat presented by the Germanic peoples was not invasion by large armies but small-scale raiding. The Romans continued to employ many of the techniques discussed in the last chapter to deal with this, joining in the patterns of intertribal warfare, but on a larger scale. Active diplomacy was combined with military action. Roman garrison commanders entertained tribal leaders to feasts and gave them gifts of money and prestige goods, emulating the methods by which powerful noblemen displayed their power in barbarian society. At formal negotiations with tribal leaders the Romans paraded their military might, the emperor receiving the envoys on a podium surrounded by the serried ranks of his splendidly equipped soldiers. Occasionally a massive attack was despatched against a people perceived to be especially hostile, settlements burnt and the population massacred or enslaved. Sometimes columns advanced from different directions to increase the element of surprise and hinder any organized opposition. Some expeditions were prepared by feats of engineering such as the bridging of the Rhine or Danube, displaying both Rome’s might and her willingness to employ massive force against her enemies. If the problems on the western frontiers seemed worse in the third and fourth centuries this was more because of Rome’s internal weakness than a result of an increased barbarian threat. Raiding grew in scale and intensity when Rome’s frontiers were perceived to be vulnerable due to her garrisons being drawn off to fight in interminable civil wars. Successful raids by one people encouraged other tribes to attack, a process which occurred without any need for tribal unification or widespread ‘conspiracies’. Rome relied on maintaining an aura of overwhelming might and invincibility to overawe her tribal neighbours. Whenever this facade was shattered by defeats, the Romans had to fight very hard to re-establish it.
One role of the limitanei was to cope with small-scale raids, and their widespread distribution in vulnerable areas helped them to accomplish this task. Many Roman forts of the later Empire were very small, but they allowed the army to maintain a visible presence over a large area. A recent study by H. Elton suggests that the reason why our sources never mention raids by fewer than four hundred men was that they were usually stopped by the border troops. Larger raids took time to muster, during which the Romans hoped to hear of the threat. It was difficult to intercept a large raid as it attacked. The frontier was too long and the number of Roman troops too small to prevent these incursions; there was inevitably a delay between the Romans receiving a report of an attack and the despatch of a force of comitatenses to deal with it. A raid tended to become more vulnerable in proportion to its success. As the war band gathered booty its speed of movement was reduced. If the warriors chose to ravage a wide area they were forced to split up into smaller and more vulnerable parties. Mobile columns, drawn largely from the comitatenses, moved swiftly to intercept the raiders as they withdrew. The Romans aimed to surprise and ambush the barbarians, if possible slaughtering them with minimum loss to themselves.
Much of the fighting in the west was on a very small scale. The main difficulty for the Romans was locating the often small groups of raiders and then approaching them undetected. This required great skill from the Romans’ scouting parties and a high level of initiative and ability from the Roman commanders down to the most junior levels. In 366 the scouts sent by Jovian, a magister equitum, located a group of Alamanni resting by a river after the sack of some villas. Jovian’s troops approached, concealed from view in a wooded valley, surprised the Germans as some were drinking and others dyeing their hair red, and destroyed them in a sudden attack. If the barbarians were well prepared or in a good position, then the Romans might hesitate before attacking them directly.
Jilium the Apostate (332-63) was noted for his attempt to replace Christianity with his own version of Sun worship. He had campaigned with great success against the Franks and Alamanni in Caul as a Caesar. Later he launched a massive Persian expedition, bringing together one of the largest armies employed in a foreign war during the sixth century. He was killed during a confused skirmish and the campaign ended in defeat.
Julian spent two months blockading a party of six hundred Franks who had occupied two derelict Roman forts in the winter of 357. When the Franks finally surrendered they were conscripted into the Roman army and sent to the east. It is interesting that this parry is said to have decided to stay for the winter in Gaul because, since Julian was too preoccupied fighting the Alamanni, they believed that they would be able to loot the surrounding area unmolested.
In nearly every case tribal attacks were not intended to seize territory but to gather booty and retire. Sometimes the approach of a Roman force was enough to persuade the raiders to leave without any actual fighting. During the third century most towns in the Empire acquired fortifications, something that had rarely been seen as necessary in the past. When raids were reported and the local troops unable to cope with them, the practice was for the population to retire to fortified strongholds taking moveable goods, animals and food with them. The Germans possessed little knowledge of siegecraft and were usually unable to feed themselves for the duration of a prolonged blockade. Cities were sometimes surprised and stormed by direct assault, especially if their defenders were few, or alternatively surrendered when they despaired of relief. Letting raiders retire without suffering any defeat did little to deter future attacks. Allowing raiders to range far into the provinces before they were attacked did not represent a deliberate policy of defence in depth, but an acceptance of the army’s inability to prevent such incursions. Despite this acceptance, Roman operations were still dominated by the aggressive response to incursions, hunting down even the smallest bands and defeating them in detail. In this small-scale warfare the Romans enjoyed considerable advantages. Their organized system of logistics allowed them to feed and maintain a force in the field at any time of year, unlike their tribal opponents. German raiders relied on surprise and speed for success, but it is striking how often the Romans used these very qualities to defeat them. The preferred Roman tactics were those of concealment, rapid movement and ambush. High-quality, disciplined regular soldiers were more effective at this low level of warfare than the tribesmen whose cultural tradition was to fight in this way. A tribal band of even a few hundred let alone a few thousand warriors was an unwieldy body, difficult to manoeuvre with skill.
The military doctrine of the late Roman army seems to have become geared for this low-level warfare. The Romans displayed a marked reluctance to confront the German tribes in open battle if this could possibly be avoided. This is in marked contrast to the army of the early Principate which, even though it was able to adapt to lower level warfare, usually seized any opportunity to face the enemy in battle. As we have seen, the unit structure of the earlier army, especially the legion of five thousand, was well suited to pitched battle, but by the fourth century the army was structured around much smaller basic units. Blocks of five thousand men were no longer useful sub-units in field armies which were tending to become quite small. Julian led thirteen thousand men at Strasbourg, and it seems unlikely that Valens had much more than twenty thousand at Adrianople. These were both very respectable armies for the period and it is likely that most campaigning was carried out by significantly smaller forces. Relatively small transfers of four to six units between field armies seem to have had considerable significance. For most operations planned to harass Germanic raiders, small forces of a few thousand were far more suited to the task, being faster and easier to control. On those occasions when the tribes did muster a large army it might prove necessary to face them in open battle. The fourth-century army won far more battles than it lost, but the consequences of defeat were dreadful. Heavy losses to well-trained manpower were to be avoided, since such troops could rarely be replaced in the immediate future, but far more significant was the blow to Roman prestige. Rome’s relations with her tribal neighbours were based upon maintaining an aura of invincibility and nothing weakened this more than a defeat in battle.
The later army lacked the ability and the confidence of the earlier army with regard to pitched battles, but it is important to place this judgement in perspective. The fourth-century army was still significantly more effective in massed battles than its tribal opponents. When large forces were sent to ravage the territory of hostile tribes the object was now to create as much devastation and terror as possible to persuade the tribes to come to terms, not to provoke them into a pitched battle in which their forces could be destroyed. The later army specialized in fighting lower scale conflict because this was the task most frequently required of it. This represented the best way of employing its high- quality manpower to defeat the enemy at minimum cost to themselves and Rome’s prestige. Defeat in a small encounter did not threaten the stability of a frontier although a series of defeats might do so. It is difficult to know when this transition occurred between an army that actively sought pitched battles and one that was reluctant to fight. Our sources for the second and third centuries are so poor that any gradual change cannot be traced. It is possible that the frequent use of legionary vexillations rather than full legions suggests that much warfare was fought on a small scale even in the early Principate.