They were a warlike people, skilled horsemen, boatmen and swimmers. They were therefore excellent soldier-material. In return for the unusual privilege of exemption from "tributum" (direct taxes on land and heads that most "peregrini" were subject to), they supplied a disproportionate number of recruits to the Julio-Claudian auxilia: one "ala" and 8 "cohortes". They also provided most of the emperor Augustus' elite regiment of Germanic bodyguards ("Germani corpore custodes"), which continued in existence until AD 68. The Batavi auxilia amounted to about 5,000 men, implying that for the entire Julio-Claudian period, over 50% of all Batavi males reaching military age (16 years) may have enlisted in the auxilia. Thus the Batavi, although just about 0.05% of the total population of the empire in AD 23, supplied about 4% of the total auxilia i.e. 80 times their proportionate share. They were regarded by the Romans as the best and bravest ("fortissimi", "validissimi") of their auxiliary, and indeed of all their forces. In Roman service, they had perfected a unique technique for swimming across rivers wearing full armour and weapons.