The principles (from the Latin princeps, first) are the soldiers of the first line (hence their name) and later of the second line in a Roman legion of the first centuries of the Roman Republic. They were experienced soldiers in the maturity of the age. Their armaments consisted of a coat of mail, the Lorica hamata borrowed from the Gauls, a short sword, gladius taken from the Spanish, and one or two javelins, pilum made to twist on impact in an enemy shield to thus handicapping the opponent in his movements and preventing him from reusing it against his former owner.
After the reform of the army operated by Marius, they formed the second line in each cohort, a tactical unit smaller than the legion.