Gaius Marius (157-86B) was one of the most innovative and influential commanders of antiquity. With Marius in command of its legions, Rome prevailed on the battlefields of North Africa and defeated a two-pronged invasion of the Italian peninsula by 300,000 migrating Germanic tribesmen. The reason for this success was a series of five ground-breaking reforms through which Marius dramatically altered the demographics, recruitment, training and operation of the Roman army. In effect, Marius’ reforms changed the Roman military from a service of short-term militia into a professional standing...