Legion was a division of the Roman army. Its size varied from about 4,000 to 6,000 men during different periods of Roman history. After Rome became an empire, a general chosen by the emperor commanded each legion. Six young commissioned officers called military tribunes served under him. But the 60 veteran noncommissioned officers called centurions were the most effective and important leaders. Each centurion led a century (a unit of about 100 men).
Before the late 100’s B.C., legions were divided into maniples of 120 men each. On the battlefield, a legion formed into three rows of maniples, with the maniples positioned like the black squares on a checkerboard. Spaces as wide as a maniple were left between the maniples. This arrangement proved effective against masses of invading warriors and against enemy forces advancing in tight ranks. The men in the front row of maniples hurled their spears at the enemy, then attacked with drawn swords. The second row of maniples charged into the empty spaces to relieve their comrades. Finally, the third row advanced with thrusting spears to secure the victory.
In 107 B.C., a general named Gaius Marius rearranged the legions into cohorts of about 400 men each. He also opened the legions to men of the lower classes, and an army of loyal, professional soldiers soon developed (see Marius, Gaius ). In the early days of the Roman Empire, the army had nearly 30 legions. These formed the backbone of the Roman army.
