Roman auxiliaries in Britain

The overall size of the Roman forces in Roman Britain grew from about 40,000 in the mid 1st century AD to a maximum of about 55,000 in the mid 2nd century.^[1] The proportion of auxiliaries in Britain grew from about 50% before 69 AD to over 70% in c. 150 AD. By the mid-2nd century, there were about 70 auxiliary regiments in Britain, for a total of over 40,000 men. These outnumbered the 16,500 legionaries in Britain (three Roman legions) by 2.5 to 1.^[2] This was the greatest concentration of auxilia in any single province of the Roman Empire. It implies major continuing security problems; this is supported by the (thin) historical evidence. After Agricola, the following emperors conducted major military operations in Britain: Hadrian, Antoninus Pius, Septimius Severus, and Constantius I.

The early 2nd century may be summarised as follows:

Of the auxilia units stationed in Britain, none was originally native British (it was the custom not to deploy units in their home country or region). However, the majority came from the geographically and culturally close areas of northern Gaul and lower Rhineland (e.g., Batavi and Tungri. Although local recruitment resulted in a growing British element in these regiments, the Batavi at least continued to recruit heavily in their native area and inscription evidence supports the view that many regiments had an international membership.^[4]

An important deployment of auxiliary regiments in Britain was to garrison the forts and milecastles on Hadrian's Wall, outpost forts and supply routes. This focus switched to the Antonine Wall in Scotland for the period it was held; however, a number of forts in the Lowland area of Scotland were garrisoned throughout the 2nd century.^{[citation needed]}