Roman army of the late Republic

The Roman army of the late Republic refers to the armed forces deployed by the late Roman Republic from the end of the Social War (91-88 BC) to the establishment of the Roman Empire by Augustus in 30 BC.

The main sources for the army's organisation and practices in this period are the publications De Bello Gallico and De Bello Civili, begun by the Roman general Caius Julius Caesar and finished by his subordinates.

The army of the late Republic constitutes the transition from the Roman army of the mid-Republic (ca. 300-80 BC), which was a temporary levy based on adult male conscription of citizens, to the Imperial Roman army of the Principate, which was a standing, professional force based mainly on volunteer recruitment.

After the end of the Social War in 88 BC, all of Rome's Italian socii ("allies") were granted full Roman citizenship, ending the dual structure of legions alongside non-citizen alae. The latter were abolished, and the Italian allies were henceforth recruited into the legions. The non-Italian allies that had long fought for Rome (e.g. Gallic and Numidian cavalry) continued to serve alongside the legions but remained irregular units under their own leaders.