The Roman military force was called a legion. As the military doctrine and capability of Rome evolved, so did the Legion. At first, it was a name used to refer to the entire Roman army. As the army became more organized, legion came to mean a fighting force of five to six thousand members. During the peak of Roman military might, the basic unit was a Centuria, an 80 man unit when at full strength. Next was a Cohort, which had 6 Centuria plus a cavalry unit, usually 20 to forty members. The Legion had about ten Cohorts, so it was about 5,400 troops. Since "legion" always meant a large number, the word came to mean a group of people with many members.
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