The auxiliary troops of the Roman army made up a vast portion of the fighting capability of the Roman army. Made of non citizens the main prize for enrolment into the army for these people was citizenship at the end of their term of service. The auxillia represented the highly diverse fighting system of Rome's army during the 1st and 2nd Century. The ranged from lightly armed companion troops such as archers and slingers to cavalry and spearmen. Generally an auxillia unit would be allowed to wear its own colours and often its own armour.
These troops are often considered of lower status or ability than their counterpart citizen armies. However in some cases the auxillia managed to defeat an enemy before the citizen legionary armies arrived on the battlefield.
It was mark of the Roman efficiency that it would allow the conquered peoples of its Empire continue to have an active role within its superstructure meaning that it always gained the strengths of a conquered people to within its ranks and could always present a diverse and specific fighting force for each situation it faced.
We are told that the Romans did not consider themselves proficient in all areas of warfare. It was in areas such as these that the true adaptability of the Roman military system would be shown. In areas of perceived specific inability the Romans would often employ soldiers from a conquered people who were famed for their skills in these areas of lack.