By 390 BC, the Roman army was in need of change, as Greek-style tactics of fighting with a heavy infantry phalanx were proving increasingly outdated. A military revolution was born in the form of the legion, a tool of war better suited to aggressive action. Yet by the end of the 3rd century BC, Rome's prestige was shattered by the genius of Hannibal of Carthage, causing the Romans to revise their battle tactics once more, this time by inventing a whole new kind of soldier. This book reveals these two defining moments in Roman military history and the revolution in battle tactics that they caused, examining how the Roman army eventually became all-conquering and all-powerful.