There is some evidence of possible exploratory expeditions during the time of Gnaeus Julius Agricola, although the interpretation of this is a matter of debate amongst historians. In places like Drumanagh (interpreted by some historians to be the site of a possible Roman fort or temporary camp) and Lambay island, some Roman military-related finds may be evidence for some form of Roman presence. The most commonly advanced interpretation is that any military presence was to provide security for traders, possibly in the form of an annual market where Romano-British and Irish met to trade. Other interpretations, however, suggest these may be merely Roman trading outposts, or native Irish settlements which traded with Roman Britain. Later, during the collapse of Roman authority in the 4th and 5th centuries, Irish tribes raided Britain and may have brought back Roman knowledge of classical civilization.
Ireland had never been conquered by the Romans and she somehow remained aloof from the changes that radically altered British society. It was Julius Caesar who invented the myth of Hibernia, a land of winter into whose mists civilized men dared not venture. There may have been a self-serving element to this, the future emperor of the Romans justifying his own reluctance to embark on a potentially costly conquest. And while there is no evidence of any large Roman military operation against Ireland, there were plenty of traders willing to ignore the grim warnings and visit Ireland’s east coast. Harbours grew up to service the boats that carried Irish leather to clothe the Roman legions. The Irish cattle barons of the plains became rich in the process. As Ned Kelly, keeper of antiquities at the National Museum of Ireland, told me: ‘The cattle barons start getting notions of grandeur and they become the important provincial kings of early medieval Ireland. You have the establishment of dynasties at that time, and they continued in power for hundreds of years afterwards. They were looking to model themselves on the Roman emperors.’
The traffic in goods and ideas was a two-way process and the greatest Roman export to Ireland was spiritual. The faith that would come to be seen as an indivisible part of Irish identity was carried across the seas from Roman Britain, where it had become the state religion on the orders of the Emperor Constantine. Through the efforts of saints such as Patrick, Declan of the Decies and a host of others, the Roman faith was spread through the island, creating monastic centres around which faith and commerce could thrive, and where an aesthetic revolution would take place. Scholars came from the continent to be educated at the great monastery of Clonmacnoise in County Westmeath.
In AD 79 Agricola turned his attention to the north, advancing on both the western and eastern sides of Britain, laying out a series of roads and forts aimed at suppressing any resistance. He then offered reasonable peace terms to win over hostile tribesmen. Succeeding campaigns took him as far north as the Tay estuary by AD 81 and a series of forts were laid out along the Forth–Clyde isthmus. In doing this Agricola was intent on subduing the more northerly tribes, the Votadini, Selgovae and Novantae. His tactics were again to lay out a network of roads and forts. He tried to win over the tribes but his efforts had little success and he was forced to rely on military control.
About this time Agricola contemplated an expedition to Ireland, urged on by the arrival of an exiled Irish prince. Tacitus said that Agricola remarked that Ireland could be reduced and held by a single legion or a few auxiliaries. Given the warlike nature of the Irish tribes this would have been improbable and Agricola’s reputation was saved by the fact that such an invasion was never undertaken. Roman troops were never based in Ireland although a 16-hectare (40-acre) fortified promontory at Drumanagh near Dublin has been claimed to be a Roman fort. It could equally well have been a trading settlement. Other Roman finds in Ireland also indicate that there was some trade between the two areas.
In his biography of Agricola, the historian Tacitus writes:
“In the fifth campaign, Agricola, crossing over in the first ship, subdued, by frequent and successful engagements, several nations till then unknown; and stationed troops in that part of Britain which is opposite to Ireland, rather with a view to future advantage, than from any apprehension of danger from that quarter. For the possession of Ireland, situated between Britain and Spain, and lying commodiously to the Gallic sea, would have formed a very beneficial connection between the most powerful parts of the empire. This island is less than Britain, but larger than those of our sea. Its soil, climate, and the manners and dispositions of its inhabitants, are little different from those of Britain. Its ports and harbors are better known, from the concourse of merchants for the purposes of commerce. Agricola had received into his protection one of its petty kings, who had been expelled by a domestic sedition; and detained him, under the semblance of friendship, till an occasion should offer of making use of him. I have frequently heard him assert, that a single legion and a few auxiliaries would be sufficient entirely to conquer Ireland and keep it in subjection; and that such an event would also have contributed to restrain the Britons, by awing them with the prospect of the Roman arms all around them, and, as it were, banishing liberty from their sight.”
During the republic the Romans had created an efficient fighting machine, which resulted in the inexorable expansion of Rome until the second century ad. The Emperor Augustus, aware of the power of this force, began a series of reforms which created a professionally paid army, loyal to the emperor, and provided an officer class drawn from the senatorial and equestrian orders, following a career structure (cursus honorum) that included holding successive military and civil appointments. The underlying assumption was that Rome’s military might was superior to any opposing force, both in her fighting techniques and by the fact that Rome was destined to rule the known world.
The Romans were a practical people. Military superiority was achieved by adapting and changing tactics, and by utilizing the manpower of other areas. Thus men from the provinces were enrolled into the army either individually or in tribal groups, some keeping their own methods of fighting so that in the auxiliary forces provincial customs and habits were accepted. Cavalry units especially were recruited from such sources and provided an essential complement to the legions, which were almost entirely composed of infantry. Native forces were recruited as professional troops and this subtly began to alter the relationship between the military and the civilian. This could be both a strength and weakness as it was uncertain where loyalties would lie. This polyglot force had to be moulded into one serving emperor and empire. In addition, it was relatively unusual for ordinary soldiers to change units and, if a unit stayed too long in one area, the men might become embedded in the community. Legion XX was established at Chester about AD 87. Although vexillations were sent to build the Hadrian and Antonine Walls and to keep order in the north, the legion remained at Chester until probably the fourth century AD. Some of the wall garrisons remained in place for many years.
The Roman military force at its greatest in Britain has been estimated to be between 50,000 and 55,000 men. Aulus Plautius had arrived with 20,000 legionaries and auxiliary soldiers with nominal strengths of 500 or 1,000 men. But legions and auxiliary forces were brought into or removed from Britain as circumstances demanded. The largest number of troops was stationed on Hadrian’s Wall, and the Wall itself and the associated military zone contained perhaps 20,000 men. The number of troops stationed in Britain indicates that the province had to keep one of the largest provincial garrisons, probably the result of the hostility of its Celtic inhabitants and the fact that the Romans never succeeded in conquering the whole island. Hostile tribes in Scotland were never entirely subdued, although finds of Roman artefacts suggest that there may have been interaction between Romans and natives. Nor did the Romans conquer Ireland, which might have prevented later Irish raids on the western shore areas.
Hibernia Romana? Ireland & the Roman empire