Auxiliary units were attached to individual Legions as opposed to being an integral part of their structure. This attachment could last for many years. The fact
Auxiliary regiments being attached to a legion does not mean that they were not capable of, or were not permitted to, carry out operations unaccompanied. Indeed, in view of their lack of combat cavalry, it was the legions that could not campaign independently. There are several examples of major operations carried out by auxiliaries alone. On Trajan’s Column, some 20 major battle scenes are shown. Auxiliary Regiments take part in 19 of these, 12 of which they are fighting alone unaccompanied by legionaries.
The Auxiliary Regiment contains 24 models (including shields and spears) – 21 legionaries and a 3 man command group of centurion, signifer and cornicen.