A new epoch in the history of the Roman Empire began with the accession of Diocletian to the throne in A.D. 284. From that time the old names of consul, tribune, etc., belonging to the republic lost their significance, and even the senate was practically abolished. Thenceforth the empire became an oriental sovereignty. In the year 292, having previously associated with himself one colleague, Maximianus Herculius, Diocletian created two Cæsars: the one, Galerius Maximianus, to act as his subordinate in the East; the other, Constantius Chlorus, to divide the government of the western provinces with Maximianus Herculius. Each of these emperors ruled with vigor in his own territory, defending the frontiers of the empire and also suppressing such revolts as broke out within its borders. But these transformations in the empire were preparing the way for events of unprecedented nature and importance, and for the rise of an emperor destined to play a part in the history of the world quite different from that performed by any of his predecessors. This was Constantine, in whose character, throughout his life, opposing elements seemed to contend for mastery, as was shown in his treatment of the perplexing questions that arose during his reign concerning Christianity, which was persecuted under Diocletian and the old Roman religion. Of his statesmanship and his further transformation of the empire, in ways which Diocletian could not have foreseen, history has made an impressive record. But the great events of his reign, which caused it to be regarded as the inauguration of a new era, were his conversion to Christianity and the acts whereby he secured its toleration and then its supremacy in the empire. In the account which follows it is clearly shown by what steps these results were attained, and how the work of Constantine the Great became the chief agency by which Christianity mounted the throne of the Cæsars.