Soon after the Caudine Forks fiasco, where Roman citizens had suffered the humiliation of being forced to pass under the yoke, an act symbolising their loss of warrior status, the tactical formation adopted by the Roman army underwent a radical change. Introduced as part of the Servian reforms, the legion had originally operated as a Greek-style phalanx, a densely packed block of citizens wealthy enough to outfit themselves with the full panoply of an armoured spearman or hoplite. The function of a hoplite had been the privilege only of those who owned a certain amount of property, poorer citizens serving either as auxiliaries or as servants.

Now, however, the Romans adopted the manipular system, whereby the legion was split into distinct battle lines, each consisting of tactical subunits, the maniples. In contrast to the one solid block of the phalanx, the legion was now divided into several small blocks, with spaces between them. The Romans, in other words, gave the phalanx 'joints' in order to secure flexibility, and what is more, each soldier, or legionary, had twice as much elbow room for individual action, which now involved swordplay instead of spear work.

Even though still a citizen militia recruited from property owners supplying their own war gear, it was the manipular legion that faced Pyrrhus and his elephants, the Gauls and their long swords, Hannibal and his tactical genius, the Macedonians and their pikes, to name but a few of its formidable opponents.