After the 50-year chaos of the mid-3rd century AD, Emperor Diocletian (r. AD 284-305) and his successor, Constantine I (r. AD 306-37), the first Christian emperor, undertook major administrative reforms to reflect new realities and improve defensive strategy. These changes saw the Roman Army completely reorganized, with its old structure of legions and auxiliary units giving way to central mobile field armies and various classes of garrison troops. In addition, the Army also began recruiting 'allied barbarians' in ever-increasing numbers and even promoted some to the level of senior command.

Roman military expert Raffaele D'Amato draws on the latest archaeological and written evidence to explore this turbulent final period of the Western Empire. Illustrated with photographs and drawings of surviving artefacts and imagery, this latest entry in a series charting the Roman Army's evolution also features eight newly commissioned colour plates depicting the uniforms and weaponry of Rome's reformed military.