Rome didn’t originally have frontiers. Virgil described an Empire without limits, so were the frontiers symbols of failure, that there were limits?
In the early Empire forts were lightly defended. Given Roman soldiers’ reputation they did not expect to be attacked.
Roman frontiers differed between those in the Near East and elsewhere. In the Near East they faced an equivalent foe, the Parthians and, in due course, the Sassanians, with whom peace was made by treaty. There were existing roads and towns with legions based there or nearby.
Elsewhere there were frontiers of inequality. Treaties were imposed, restricting settlement beyond the frontier and freedom to enter Roman territory. New roads or tracks were built to link forts, with the effect that roads circled the Imperial frontier. Agriculture and settlement were attracted to the frontier supplying the army and providing an example of prosperity and peace to tribes beyond it.
In Arabia and Africa there were limited fortification marking the frontiers, as beyond the limits of settlement and agriculture was desert.
The purposes of frontiers
< A base for further operations. The Roman army was offensive not defensive in function. By spreading forces over a frontier their effectiveness would have been dissipated. Numbers were insufficient to man walls. Roman soldier’s equipment was not really suitable. Turrets were for signalling. Hadrian’s Wall did not include a walkway, or fighting platform. If faced by an enemy the Roman Army would march out to fight, not slink behind the walls
< To prevent raiding & banditry
< To monitor & control those in the border area, preventing free movement and controlling the flow of goods beyond the empire evidenced , in some cases, by the lack of Roman goods.
< Controlling access to the empire. Like the Berlin Wall it was essentially to control the movement of people cf the present position with illegal immigrants. The intention was not to stop armies but individuals & groups of people.
< Mark where the Roman Empire began. Crossing it, except where allowed, was evidence of intention.
< Symbolic. The very size etc of Hadrian’s Wall was making a statement.
<Passport & customs dues control
Hadrian built a Greek style wall in Britain. It was too long to do this on German frontier. Breeze argues the distinctive qualities of the Hadrian & Antonine Wall don’t mean they were defensive but reflects Hadrian’s intervention. The Wall was built on the limits of a large militarised area with legionary forts at Chester & York on navigable rivers. In Britain does the size of the military reflect that this was unfinished work? In Britain there was defence in depth given its narrowness & continuing military occupation
Dacia was a natural amphitheatre surrounded by the Carpathians, Transylvania. Like Britain it was a bulge in Rome’s frontiers. In Dacia foot soldiers guarded passes, cavalry were behind with legions at the province centre.
Germany across the Rhine was occupied between 9 BCE & 9 CE until the Governor Varus was killed with 3 legions The legions retreated across the Rhine waiting for an order to advance that never came. Gradually army groups were broken up & units spread along the river. This may not just have been for security reasons but also so it was easier to gather local supplies. Overtime distances between forts was reduced to 11 km, half a day’s march
During the reign of Gallienus the frontier was pulled back to the line of the Rhine & Danube. Important markers they were used by the Romans for supply, effectively they became the frontier by becoming a hindrance to further advance, which were crossed by barbarians when frozen or rivers were running at low levels.
The Roman fleet operated in the rivers as part of the army. On the Danube there was one above & another below the Iron Gates. There was another on Lake Constance.
310 Constantine built bridges over the Rhine & Danube at a legionary fort with another fort on the opposite bank. Generally when Roman armies crossed rivers bridges had to be built, showing rivers were treated as frontiers.
There were towers along the upper Rhine as close as 1-2km apart. There were also fortified landing places, usually two, one on either bank, behind the lines supply granaries.
The Euphrates frontier was different as there Rome was taking over existing states.
Where a river cut through gorges eg on the Danube & Euphrates there were were significant impediments reducing the need for extra defences. There were Forts at each end and at each end of sluggish/ marshy areas.
Breeze generally thinks the importance of rivers & seas has been underestimated.
In the late 3rd/early 4th centuries Diocletian’s reorganisation of the army created new field armies, units on frontiers becoming second class troops. Emperors & their deputies were no longer at Rome but on or closer to frontiers. It was defeat of the mobile field armies which spelt the end.
Under Diocletian & Vespasian forts changed. They became taller & were no longer so regular in shape. Instead of being on low hills or slightly raised ground, as were earlier forts, they were placed on higher more defensible ground. They had thicker walls, bastions & two single portal gates rather than four double portal entrances, indicating defence was more important. Sometimes barrack blogs were built against the inside face of walls. Some fortified fortlets occupied a fraction of the space of the earlier fort. These were moves towards what became normal in the Middle Ages.
David Breeze is an archaeologist, who has written extensively about the Roman army and about Hadrian’s Wall and the Antonine Wall. He was responsible for the successful bid for the latter to be recognised as a World Heritage Site.
The book is extensively illustrated with maps, diagrams and plates. At times repetitive, it would have been better if substantially re-ordered. That it is a relatively difficult read is a pity as It includes some interesting ideas.