Rome moved from the phalanx toward manipular formations better suited to Italian terrain. Its infantry differed in age, experience, and equipment, with the wealthy and experienced triarii at one end and younger troops at the other. Early in the naval war, the Romans appear to have preferred principes as marines. Their experience and heavier equipment made a secure corvus crossing useful. Hastati and velites took a greater share of marine duties as the conflict continued. Their lighter equipment and different fighting methods provide another suggested reason for abandoning the bridge.
Chapter · 56:42-59:09
Rome adapts its manipular army for fighting at sea
The choice of principes as early marines made the corvus a bridge between Roman infantry experience and an unfamiliar naval battlefield.