The significance of military reforms in the Julio-Claudian period can be seen best by first looking at the changes, and then deducing how these changes affected the nature of the principate.

During the reign of Augustus, the republican army was in great need of reform for a number of reasons.

Firstly, there was no real standing army to man the vast frontier regions of the empire. Secondly, the burden of military service rested too much on the Italians, and so Augustus' immediate task was to reduce the army to an effective size. He achieved this through two major demobilisations; one in 30 and the other in 14. The sixty legions involved in the civil war between himself and Antony were reduced to twenty-eight, and after the Varian Disaster in AD 9, where three legions were lost, the number was reduced to twenty-five...