Marian reforms
The original Roman army was made up of hoplites, whose main strategy was forming into a phalanx. By the early third century BCE, the Roman army would switch to the maniple system, which would divide the Roman army into three units, hastati, principes, and triarii. Later, Marius would institute the Marian reforms, creating the Roman legion of popular imagination. Eventually, Roman emperor Diocletian would create the Comitatenses and Limitanei units to better defend the empire.