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Gravestone of the Centurion Marcus Caelius

Augustan reorganisation

Augustus (ruled 31 BC - 14 AD) was able to establish the Roman army on a permanent, financially manageable footing. The number of legions was reduced from 60 to 28 (then down to 25 in 9 AD), and numerous colonies were established in Italy, in the more Romanised provinces and in areas which required tight control. Colonies became an important source of future citizen recruitment.

Legions were grouped initially in regions which were not fully subdued, such as Spain and the Balkans. But in the longer term they were poised for future expansion, as in Germany and Syria. Alongside the legions there were non-citizen regiments, permanently established on the model of legionary cohorts for infantry, and similar sized units (alae) for cavalry.

Collectively known as auxilia, these units exploited the regional military traditions of the empire and its fringes to supply cavalry, archers, and light troops. They were commanded by equestrian officers - more politically reliable than the senators whose social standing was necessary for commanding citizen troops. Senators governed provinces and commanded legions, but Augustus was careful to limit their terms in office and to fill sensitive posts with equestrians, such as command of the newly formalised Praetorian Guard.