Fundamental problems with the empire still remained. The right of imperial succession had never been clearly defined, which was a factor in the continuous civil wars as competing factions in the military, Senate, and other parties put forward their favored candidate for emperor. The sheer size of the empire, which had been an issue since the late Roman Republic three centuries earlier, continued to make it difficult for a single ruler to effectively counter multiple threats at the same time. These continuing problems were addressed by the radical reforms of Diocletian, who broke the cycle of usurpation. He began by sharing his rule with a colleague, then formally established the Tetrarchy of four co-emperors in 293. Historians regard this as the end of the crisis period, which had lasted 58 years. However the trend of civil war would continue after the abdication of Diocletian in the Civil wars of the Tetrarchy (306-324) until the rise of Constantine the Great as sole Emperor. The empire survived until 476 in the West and until 1453 in the East.