Alongside the legions, Augustus established the auxilia, a regular corps of similar numbers to the legions, recruited from the "peregrini" (non-citizen inhabitants of the empire – about 90% of the empire's population in the 1st century). As well as comprising large numbers of extra heavy infantry equipped in a similar manner to legionaries, the auxilia provided virtually all the army's cavalry (heavy and light), light infantry, archers and other specialists. The auxilia were organised in c. 500-strong units called "cohortes" (all-infantry), "alae" (all-cavalry) and "cohortes equitatae" (infantry with a cavalry contingent attached). Around 80 AD, a minority of auxiliary regiments were doubled in size. Until about 68 AD, the auxilia were recruited by a mix of conscription and voluntary enlistment. After that time, the auxilia became largely a volunteer corps, with conscription resorted to only in emergencies. Auxiliaries were required to serve a minimum of 25 years, although many served for longer periods. On completion of their minimum term, auxiliaries were awarded Roman citizenship, which carried important legal, fiscal and social advantages. Alongside the regular forces, the army of the Principate employed allied native units (called "numeri") from outside the empire on a mercenary basis. These were led by their own aristocrats and equipped in traditional fashion. Numbers fluctuated according to circumstances and are largely unknown.