The Dominate or late Roman Empire was the "despotic" later phase of imperial government, following the earlier period known as the "Principate", in the ancient Roman Empire. It has traditionally been considered to begin with the commencement of the reign of Diocletian in AD 284, following the Third Century Crisis of AD 235–284, and to end in the west with the collapse of the Western Empire in AD 476, while in the east its end is disputed, as either occurring at the close of the reign of Justinian I (AD 565) or of Heraclius (AD 641). In form, the Dominate is considered to be more authoritarian, less collegiate and more bureaucratic than the Principate from which it emerged.