List of Roman auxiliary regiments

The rule of the first emperor, Augustus, (30 BC–AD 14) saw the foundation of the majority of the regiments attested in Hadrian's time.

In the earlier part of this period, regiments were raised from and named after individual tribes, for example Campagonum, Trevirorum and Bessorum.

For example, the cohors II Gallorum veterana equitata must have recruited a calculated 8,000 soldiers over its probable lifespan of about 250 years but the origins of only two rankers are known.

According to Holder, during the Julio-Claudian dynasty (AD 14–68), regimental ethnic identity was preserved to some extent, with evidence of continued recruitment from the original people.

By the time of Hadrian, however, a regiment's name, in most cases, probably represented the ethnic origin of few, if any, of its members.

This is because during the Flavian dynasty (AD 69–96), as a matter of deliberate policy, most regiments were deployed in provinces far from their original home and drew the majority of their recruits from local natives and the rest from all parts of the empire.

A regiment deployed long-term in the same province would thus, over time, acquire the ethnic character of its host population.

In the Augustan era, commanders of auxiliary units were often Roman legionary centurions, or native chieftains.