By 390 BC, the organization of the Roman army was in need of change. Fighting in the Greek-style with a heavy infantry was proving increasingly outdated and inflexible, resulting in the Roman's defeat at the hands of the Gauls at the battle of Allia. Following on from this catastrophe and in the next fifty years of warfare against Gallic and Italian tribes, a military revolution was born: the legion. This was a new unit of organization made up of three flexible lines of maniples consisting of troops of both heavy and light infantry. However, at the end of the 3rd century BC, Rome's prestige was shattered once more by the genius of Hannibal of Carthage, causing Roman battle tactics to be revised again. The legendary general Scipio Africanus achieved this, finally destroying the Carthaginian army at the climactic victory of Zama. A wholly new kind of soldier had been invented, and the whole Mediterranean world was now at Rome's feet. This book reveals these two defining momentsin Roman military history and the revolution in battle tactics that was the result, examining how the Roman army eventually became all-conquering and all-powerful.