The history of Rome is closely tied to its military history. As a fledgling nation, Rome's military was disorganized and sporadic, only being brought together as it became necessary. With time, however, the military would become a professional war machine, with its members fighting for the glory of the state, rather than for personal acclaim.

The expansion and fall of the Roman Republic and the rise of Imperial Rome can all be attributed in part to shifts in military structure, loyalty, and purpose. A look at the history, practices, and composition of the Roman Army from the early Republic to the Roman Empire will follow.