Waldgirmes Fort in Hessen

Most frontiers did not have a continuous boundary such as Hadrian’s Wall. This map of the forts and fortresses along the frontier in Germany at the end of the 1st century AD provides an example of more typical frontier systems. Only a few stretches were provided with linear fortifications.

Roman River Patrol Vessel

In addition to their urban fortifications, the Romans also constructed ramparts, palisades, stone forts, and watchtowers along the exposed frontiers of their empire to limit incursions by hostile tribes. The most extensive and famous of these were the limes of the German frontier where it diverged from the Rhine and Danube rivers and required marking, them-selves a deterrent to invasion; and Hadrian’s Wall in northern England, to isolate the northern part of the island which the Romans considered incapable or unworthy of conquest.

Roman military sites are best known from the western empire locations. In fact, a general tendency in the scholarship of the western Roman Empire is to concentrate on military history, so there is a somewhat skewed view of the importance of military sites in that region. The features of a Roman military camp or fort were quite standard. But there were also important permanent military settlements in the Roman frontier that should be mentioned. Of importance to Roman conceptions of the frontier is the concept of the limes, the border of Roman control. This border was conceived as a line, with everything behind the line conjuring up images of civilization and urban life, and everything beyond the line conjuring images of barbarians and unsettled societies. Perhaps the best physical example of this Roman sensibility is Hadrian’s Wall. But borders in other parts of the empire have also been identified. Most conspicuous are rows of watchtowers (built of stone and/or timber) that allowed Roman soldiers to guard the surroundings. Forts and garrisons were also important Roman military settlements, and the rate of their establishment corresponded with the expansion of the empire. Related to these permanent military settlements were the towns that arose in adjacent land, filled with individuals whose economic livelihoods were geared toward servicing the Roman soldiers. Because Roman soldiers could expect consistent and good payment, these subsidiary services could be supported over the long term.

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The Romans did not really have a word equivalent to our ‘frontier’. Limes, a Latin word which used to be understood in this sense, largely kept its real meaning of road. Roads were fundamental to any long-term military deployment, connecting individual army bases. Good, all-weather roads made possible rapid and efficient movement of troops and supplies. As stated earlier, Roman forts and fortresses were not primarily defensive structures in the sense that it was rare for their garrisons to fight from behind their walls. The army was usually better trained and disciplined, and had a more sophisticated command structure, than its opponents and was often also better equipped. This gave considerable advantages in open fighting, which could and did compensate for much smaller numbers. Therefore when attacked, Roman units left their fortifications at every opportunity to fight the enemy in the open. The road system facilitated the concentration of units to form a field force.

Several frontier zones were based around significant geographical features, if only because these had often determined pre-existing political geography. Much of the frontier in Africa was formed when the Roman province reached desert areas which were sparsely populated and difficult to cross. The Rhine and Danube in Europe, and Euphrates in Syria, formed important parts of the frontier system in each area. Rivers were patrolled by Roman vessels and transport of men and material by water was often more rapid than overland. They also presented barriers to an invader, especially since the army took care to guard any bridges. A large army would be delayed by a river, since it would need to carry with it, make or gather many boats to ferry itself across. Any delay gave the Romans more time to discover the incursion and gather a force to meet it. Only freak weather conditions, such as the occasional freezing of a river in winter, changed this. Yet these same rivers did not form significant obstacles to the Romans. They controlled the bridges and crossing places, and their navy was active on the water itself. A Roman army faced little inconvenience whenever it wished to advance suddenly and rapidly across a river line against the enemy. Frontier lines were essentially solid bases from which the army could launch an offensive or counter-offensive whenever it desired, not barriers to hinder movement in both directions.

Auxiliary forts tend to be arranged in a line on or near the road running along the fringe of the province. Positions of obvious importance, for instance mountain passes, water sources in desert areas, and river crossings, were usually protected by a fort. There was also a range of smaller military bases, from forts and fortlets for small vexillations to small turrets (turres and burgz) manned by no more than a handful of soldiers. The turrets were a feature along many Roman frontiers, as well as along important roads, and are depicted on Trajan’s Column. In some cases they appear to have been simply observation posts, providing raised viewing platforms and also contributing to the army’s visible presence to surrounding land. Such lines of towers may well have helped to suggest that the army was watching what occurred. In some cases the towers were part of a system for signaling simple messages, using either fire signals or basic forms of semaphore. Observation from fixed points provided the army with some information, but far more could be derived from patrols. One reason for the high proportion of cohortes equitatae in relation to purely infantry units was that the small, balanced force of foot soldiers and cavalrymen were especially well suited to the patrolling and escort duties required of frontier garrisons. In desert areas some mixed cohorts acquired a small number of camel riders (dromedarii), who were especially suited for long-distance patrolling in the arid conditions. At least as important as anything that parties of soldiers themselves saw or heard was the diplomatic activity which went on well beyond the military zone. Frequent embassies to and from Parthia and later Persia are mentioned, but we also read of centurions sitting in on the gatherings of tribal chieftains in late 2nd-century Germany. Friendly leaders often received subsidies, and sometimes military advice or actual aid.

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