Diocletian was Emperor of Rome from 284 until 305, who reformed the administrative machinery of the empire, introducing the two-tiered system of Augusti and Caesars. Diocletian was born of humble parents in Dalmatia and became an officer in the Roman army. When he became emperor he was immediately faced with uprisings in many parts of the vast empire. Implementing his new system, he selected as his colleague Maximian, giving him the title of Caesar and, later, of Augustus.
Needing more assistance in defending and administering the empire, and also in order to assure a peaceful succession to the throne, Diocletian selected two more colleagues, each with the title of Caesar, Galerius, adopted by Diocletian, and Constantius I, who was adopted by Maximian.
The empire was divided into managerial regions, but all edicts were signed jointly by the four rulers, with Diocletian retaining his supremacy. The new system was an unqualified success, maintaining order and generating military victories, and ended forever the primacy of Italy.
In 305 Diocletian abdicated his power and forced Maximian to follow suit. Leaving the succession, as he had planned, to Galerius and Constantius, Diocletian retired to Salona, in Dalmatia.