ABSTRACT
For the Roman world the later third century was a period of insecurity and chaos, with emperors often reigning for brief periods before meeting a violent end. But Diocletian (emperor 284–305) put the Empire on a road to recovery, and his reign and that of Constantine I (306–37) are taken as marking the transition from the Early (or High) Empire to the Late (or Low) Empire. Undoubtedly to observers at the time the transition would have seemed more gradual, but there can be no doubt that the years between 285 and the 330s saw important administrative as well as religious changes. The Empire, as Diocletian realized, was often too beset by internal disorders and external threats for a single emperor, however energetic and resourceful, to govern alone. It had not grown any larger in the preceding century and a half, but was increasingly buffeted by foes. The solution, as Diocletian saw it, was an element of power-sharing, which had indeed been tried before between an emperor and a son or brother. In 286 Diocletian selected as co-Augustus a fellow-soldier Valerius Maximianus (Maximian) and a few years later each Augustus appointed a Caesar to assist him. This was government by committee, with a clear hierarchy and spheres of geographical responsibility.
