For most of the period between the invasion and AD 410, Britannia had either three or four legions based at the three principal fortresses of Isca (Caerleon), Deva (Chester) and Eboracum (York). The army also included an approximately equal number of auxiliary troops garrisoned in smaller units in a network of forts. This means that there were between 40-50,000 soldiers stationed in Britannia, one of the largest armed forces in the Empire.

However, after the conquest, soldiers did not just provide military force. They kept the peace, helped in the administration of the province, and undertook engineering programmes such as road-building or constructing fortifications. When the emperor Claudius (reigned 41-54) invaded Britain in 43, his army included four experienced legions. The history of one of these legions in Britain, the IXth, shows how diverse a legionary soldier’s career could be.

In the early 50s the base of the IXth legion is not known for sure, but may have been a temporary fortress at Longthorpe, near Peterborough. During the Iceni revolt of 60-1, the legion suffered such heavy losses that it had to be reinforced with 2000 men from the Rhine provinces. From the early 60s it was at Lindum (Lincoln), and in the early 70s, moved to Eboracum (York), where it took part in the pacification of the north. In the early 2nd century it left Britain for mainland Europe.