The frontiers

The greater part of the Roman army, especially in the western provinces, was based in the frontier zones. There has been considerable debate over the role of the army in these areas, and indeed of the Roman concept of frontiers, but it is very important to note that the Empire’s frontiers did not represent clear geographical limits to the army’s activity. The Romans were heavily involved both diplomatically and militarily for a considerable distance beyond the boundaries of the provinces. Centurions attended tribal meetings of many of the peoples of north-west Europe. Noblemen thought to be favourable to the Romans were paid large subsidies, allowing them to support a bigger band of followers and increase their status within the tribe. Ideally, this deterred the tribes from large-scale aggression, and at the very least it gave the Romans advance warning of its likelihood. Warfare and especially raiding played a central role in the society of many of the peoples outside the frontiers in Britain, Germany and along the Danube. Status within a tribe came from success in war, and attacks against the Roman Empire brought tremendous prestige as well as the prospect of considerable loot. Our sources usually only mention the very large raids by thousands of warriors which penetrated deep into the peaceful provinces. Most barbarian military activity was on a smaller scale; a nobleman and his immediate retainers plus as many other warriors as were attracted by his prestige, probably no more than a few hundred men in total. Some incursions may have been even smaller. There did not need to be any specific motive for such attacks, any more than there needed to be a motive for the constant intertribal raiding. Tacitus claimed that German tribes liked to maintain a depopulated area around their territory to deter enemies by this symbol of prowess and to give more warning of approaching raiders. In themselves such small-scale incursions did not threaten the stability of the Empire, but the danger if they went unchecked was that a perception of Roman vulnerability would encourage an escalation in the size and number of attacks.

Opposite: The Nabataean kingdom was one of the wealthiest of the Client States which were a prominent feature on the Roman frontiers, especially in the east. Its capital at Petra is famous for its spectacular civic buildings and tombs. It was annexed by Trajan who created the new province of Arabia.

The number of Roman troops was very small in relation to the size of most of the frontier areas which they occupied. The army lacked the capacity to intercept every raid. One solution might have been to conquer and incorporate the hostile tribes into the Empire. Domitian sought to control the Chatti by advancing the frontier and building a line of forts in their territory. However, conquest required large numbers of troops, most of which would then be tied down as garrisons, and anyway expansion under the Empire needed to be carefully supervised by the emperor. Ideally, diplomatic activity reduced the hostility of the tribes, but often this had to be combined with military force. If the Romans could not stop the raids then they could ensure that the tribes responsible did not go unpunished. Fast-moving columns of troops, stripped of unnecessary baggage and carrying only enough supplies for the duration of the expedition, launched sudden attacks on the tribes, burning their settlements, destroying their crops and rounding up livestock. Only a small area would feel the actual effects of such a punitive expedition, but it demonstrated that the Romans could and would punish attacks upon them with appalling ferocity. Mustering a tribal army took time, and if one did muster to confront the Romans it was usually only when they were withdrawing. A competently handled Roman force could expect to overcome significantly larger tribal armies, so that often a defeat in battle was added to punishment inflicted.

The Roman Empire in AD 114

The Roman Empire reached its fullest extent under the Severans. Since the first century ad the emphasis of the army in Europe had shifted from the Rhine to the Danuhiatt frontier and there were now only four legions in the German provinces. The vast majority of units continued to be stationed in the frontier provinces, with the exception of the Syrian and Egyptian legions who covered the great cities of the east. There was also now a legion permanently stationed outside Rome which, with the addition of the Guard units, provided the Emperor with the basis of a powerful army. Apart from new legions and the troops stationed in Italy, nearly all legionaries were by this time born in the provinces.

In a sense the Romans had joined in the traditional patterns of intertribal warfare, with the distinction that their attacks were on a more massive scale.

With their better organization and logistic support the Romans were also able to attack at any time of the year, usually with the benefit of surprise. The flexibility of the Roman military system allowed them to adapt to fighting different cultures. If a people possessed a strong field army and a willingness to fight open battles, then the defeat of this force usually ensured their surrender. If they possessed important political and economic centres, such as cities, then these were besieged and captured. A people who refused battle or lacked large, important settlements faced attacks on their villages, their cattle and crops. One of the most important symbols of wealth in Germanic society was cattle, making their capture a valuable way of applying pressure on tribal leaders. The Romans were aware of the respect accorded to noblewomen in German society, and as a result demanded these as hostages. Punitive raids were at best temporary solutions to the problem, lasting only as long as the fear they created, while the memory of burning villages ensured a legacy of hatred so that each new generation added the Romans to the list of a tribe’s enemies. The Romans needed to maintain an appearance of overwhelming power, since any perception of weakness, such as the reduction in size of a frontier garrison or, even worse, the smallest Roman defeat, risked a return to general hostility.

More common than unbroken boundaries such as ditches or walls were systems of small outposts, like this watchtower on the River Danube depicted on Trajan's Column. These were used to pass signals, hence the wooden pyre and piles of straw ready to be ignited. Other similar installations were built along the line of road systems policed by the army, for instance in Egypt.

Roman frontier zones were always based on good communications, usually by road, but also along rivers such as the Rhine and Danube. Bases were established along the line of these routes, allowing swift concentration of forces. Auxiliary forts accommodating single cohorts or alae were located further forward, with the great legionary fortresses some distance to the rear. By the end of the first century most of the early turf and timber forts constructed by the Romans were being replaced by more permanent stone structures. The garrisons of these forts were not static and it is now clear that detachments of legionaries and auxiliaries were freely mixed in the forward areas. Often little more than a unit’s records and administrative HQ were permanently in residence at their base and the bulk of the unit might be far afield. In the late first and early second century the concept of a line of bases linked by a road was taken a stage further and linear barriers were constructed. The most famous example is Hadrian’s Wall running across northern Britain between the Tyne and Solway, but other linear systems were constructed in North Africa, and covered the gap between the Rivers Rhine and Danube. Most of these structures were relatively simple combinations of ditches, ramparts and palisade walls linking together small outpost fortlets and watchtowers. On Hadrian’s Wall there were small fortlets, or milecastles, every Roman mile, and two small turrets in between. Most of these walls were not topped by walkways and it is not even certain if this was the case with Hadrian’s Wall. In some areas lines of small watchtowers were built without the connecting wall.

The Frontiers in northern Britain

Archaeological records tell us that a line of forts running along a road known now as the Stanegate was replaced by a solid wall under Hadrian. This was later replaced by the more northern Antonine Wall, which was itself abandoned and re-occupied before the army finally returned to Hadrian's Wall.

The Emperor Hadrian presents a sacrificial cake or popanum to the Goddess Roma. Hadrian spent much of his reign touring the provinces, inspecting the armies and reorganizing the frontiers. In several places, most notably in northern Britain, he ordered the construction of massive linear boundaries.

Hadrian’s Wall crossing Cawfield Crags in Northumbria. The wall was constructed in several phases and a series of alterations made to the original design. Running from the mouth of the Tyne to the Cumbrian coast it included small fortlets every Roman mile, and two turrets between each one. The formula was applied with some rigidity, some gateways opening out on to almost sheer slopes. Initially the western section was built of turf and timber, but this was later replaced with stone. To the south the military zone was marked by a wide ditch, known conventionally as the Vallum. Later forts were added to the line of the wall, in some cases, as at Houseteads, being built over earlier turrets. The wall allowed the army to control all traffic passing through the region, which could only cross it at guarded gateways. It was also visually very impressive. Although the wall has been intensively studied for over a century, many fundamental questions remain unanswered. We cannot be certain of its original height, nor whether it possessed a continuous walkway allowing sentries to pace along its length.


The gateways of stone forts or fortresses were always impressive affairs and defended by towers. A recently discovered piece of graffiti from a Roman outpost in Egypt suggests that there may often have been four storeys, instead of the three shown here. However, it is important to remember that the Roman army's bases were not primarily intended as defensive sites, did not possess especially strong fortifications and were not built on formidable positions. The army of the Principate normally expected to defeat its enemies in the open and heavily outnumbered garrisons showed a willingness to come out and fight more numerous attackers.

This full-scale reconstruction of a timber gateway was built on the site of the Roman fort at Baginton, near Coventry. Until the later part of the first century ad, most Roman bases were defended by turf and timber fortifications like this, an extension of the same basic design as the marching camps built by the army on campaign.


Double gateways were the most common Roman design for all four entrances in the standard fort design, but some forts had only a single gate as shown here. The towers might be used to mount light artillery, such as the scorpion bolt-shooters. At least one or more v-shaped ditches offered further protection. The ditches have a rectangular sectioned trench running through the bottom, which facilitated cleaning out spoil, but also might trip charging attackers. Other obstacles, such as concealed pits with sharpened stakes in the centre, known to the soldiers from their shape as ‘lilies’, were common. These layers of defences would take the momentum out of an enemy attack before he reached the walls and attempted to scale them.

These great fortified lines are barely mentioned, let alone explained, in our literary sources. Our understanding of them is based almost exclusively on their archaeological remains and it is not always possible to deduce their exact function. What is obvious is that these were nor fighting platforms from which the Romans fought off the barbarian hordes who recklessly hurled themselves against the bastions of civilization. Hadrian’s Wall from its first inception included gateways and crossing points at every milecastle, and when initial plans were modified and forts were constructed on the line of the wall itself, then these added to the number of gateways. The Wall was never intended to restrict the movements of the Roman army, but simply provided a secure base for its advance. The Romans maintained permanent outposts beyond the line of the Wall and major problems were dealt with by mobile operations even further afield. It did allow the Romans to control movement through the area, since all crossing points were guarded. We know that there were restrictions placed on German tribesmen crossing the Rhine and especially on their carrying of weapons. In this way it did much to prevent the small-scale raiding which formed the bulk of military activity on the frontiers. Preventing many of these incursions discouraged an escalation of hostility into larger-scale warfare. Linear boundaries were only feasible in certain geographical conditions, but small outposts and watchtowers served much the same purpose, creating the impression that a wide area was under continuous surveillance and they helped to deter such activity. It is also worth bearing in mind the physical impression created by these structures. A fortification running from one horizon to the other was a powerful statement of Rome’s might. Caesar tells us that some Gallic tribes cultivated thick hedge lines marking the borders of their territory to deter raiders. In many areas the Romans took care to maintain an area bare of settlement for some distance in advance of the frontier. Whether the Romans intended this or not, it is likely that their frontier systems were perceived as clear demarcations of territory by many barbarian tribes. This reinforces the idea that the Romans had joined in, albeit as a massively stronger participant, the traditional pattern of intertribal warfare.

The fort at Houseteads on Hadrian's Wall is one of the most famous Roman sites in the world. This picture shows one of the granaries or stores, its floor raised on the rows of wooden pillars to keep the grain cool and deter vermin. All Roman bases had provision for the storage of huge amounts of food, sometimes up to a year’s supply.

This view shows the main buildings in the centre of Houseteads fort. Closest is the commanding officer’s house (praetorium), built in the classic Mediterranean plan around a central courtyard and including underfloor heating for some rooms. On the higher ground to the right is the headquarters (principia) where the unit's standards and records were kept and its day-to-day administration carried out. In the background is the hospital, a feature of all major bases.

The Roman army of the Principate was a relatively small but high quality force most suited to mobile operations. Its military doctrine remained intensely aggressive even though the pace of conquest had been drastically reduced and it was increasingly deployed in semi-permanent frontier zones. Measures were taken to police small-scale banditry, raiding and violence both on the frontiers and within the provinces, but the reaction to any major opposition was to assume an immediate offensive. Whatever the local situation, the Roman army adapted its doctrine, deployment and tactics to make the most of the advantages it enjoyed over its less organized and skilled opponents. The frontiers were not static defences, but bases for military and diplomatic activity reaching far beyond the provinces. The Roman military system was flexible enough to adapt to local requirements, but still retained the distinctively relentless pursuit of final victory.

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