Auxiliaries

thumb|300px|Roman auxiliary infantry crossing a river, probably the Danube, on a [[pontoon bridge during the emperor Trajan's Dacian Wars (101–106 AD). They can be distinguished by the oval shield (clipeus) they were equipped with, in contrast to the rectangular scutum carried by legionaries. Panel from Trajan's Column, Rome]] The '''''' (, ) were introduced as non-citizen troops attached to the citizen legions by Augustus after his reorganisation of the Imperial Roman army from 27 BC. By the 2nd century, the contained the same number of infantry as the legions and, in addition, provided almost all of the Roman army's cavalry (especially light cavalry and archers) and more specialised troops. The thus represented three-fifths of Rome's regular land forces at that time. Like their legionary counterparts, auxiliary recruits were mostly volunteers, not conscripts.

The were mainly recruited from the peregrini, free provincial subjects who did not hold Roman citizenship and constituted the vast majority of the population in the 1st and 2nd centuries (c. 90% in the early 1st century). In contrast to the legions, which only admitted Roman citizens, members of the could be recruited from territories outside of Roman control.