religious policy aiming at religious unity, large scale monetary reforms, and the creation of an empire-wide civil bureaucracy. Although Diocletian is commonly thought of as creator of the Dominate, its origins lie in the innovations of earlier emperors, principally those undertaken by Aurelian (AD 270–275). Some reforms stretch back to the reigns of Gallienus (AD 253–268) and Trajan (AD 98–117), during whose reign "knights were given an escalating importance in the administration of Rome and the empire." Not all the changes that produced the 'Dominate' were completed by the time of Diocletian's abdication in AD 305; many changes were either introduced or modified by Constantine I. Consequently, just as the Principate emerged over the period 31 BC through to 14 AD, it is only by AD 337 that the reforms that resulted in the Dominate were largely complete. In the opinion of the historian John Bagnall Bury, the system of government, constructed with the most careful attention to details, was a solution of the formidable problem of holding together a huge heterogeneous empire, threatened with dissolution and bankruptcy, an empire which was far from being geographically compact and had four long, as well as several smaller, frontiers to defend. To govern a large state by two independent but perfectly similar machines, controlled not from one centre but from two foci, without sacrificing its unity was an interesting and entirely new experiment. These bureaucratic machines worked moderately well, and their success might have been extraordinary if the monarchs who directed them had always been men of superior ability. Blots of course and defects there were, especially in the fields of economy and finance. The political creation of the Illyrian Emperors was not unworthy of the genius of Rome. Characteristics Multiple emperors Under the Principate, the position of emperor saw the concentration of various civil and military offices within a single magistracy. Augustus and his successors usually took great care to disguise the autocratic nature of the office by hiding behind the institutions of the Roman Republic and the fiction that the emperor was simply the princeps or first citizen, whose authority was granted by the Senate. This role was almost always filled by a single individual, and the date that the Potestas tribunicia was conferred onto that person was the point when imperial authority could be exercised. Over the course of the Principate, it became common for the emperor (or Augustus)