In the singular princeps, was armed like hastati – a short sword (gladius) and two 120 cm javelins (pila). They wore chainmail, helm, and greaves. They had to collect the equipment themselves. According to Polybius’ traduction condition of the defensive armament of hastati, principes and triarii were the same and depended mainly on the wealthiness of the soldier.
Principes were older than hastati but younger than triarii.
They were recruited out of men from 24 to 30. Like hastati, they used tactic ‘pilum-gladius’ which consists of throwing pila and then fighting with swords.
A standardized army after Marius’ reform was similar to principes based on look and equipment.
During the battle, principes were used only when the first line was beaten. Therefore principes would make a counter-attack that should crush an exhausted enemy. This manoeuvre lets hastati regroup and rest.
Principes like hastati were divided into 10 maniples 120 soldiers each.