High Quality Content by WIKIPEDIA articles! The Sacramentum was an oath taken by all Roman legionaries on entering the Roman army. In the rare case of punishment by Decimation, the surviving legionaries were often required to renew this military oath, which was the foundation of Roman military discipline. It was created by Augustus during his military reforms in the early first century. The Roman legion (from Latin legio "military levy, conscription," from legere "to choose") is a term that can apply both as a translation of legio ("conscription" or "army") to the entire Roman army and also, more narrowly (and more commonly), to the heavy infantry that was the basic military unit of the ancient Roman army in the period of the late Roman Republic and the Roman Empire.