High Quality Content by WIKIPEDIA articles! Principes (Singular: Princeps) were spearmen, and later swordsmen, in the armies of the early Roman Republic. They were men in the prime of their lives who were fairly wealthy, and could afford decent equipment. They were the heavier infantry of the legion who carried large shields and wore good quality armour. Their usual position was the second battle line. They fought in quincunx formation, supported by light troops. They were eventually done away with after the Marian reforms of 107 BC.