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, some of whom rose to positions of supreme command.
