Born Diocles, an Illyrian of low birth, he rose through the ranks to the consulship and was chosen by the Army in A.D. 284 to replace Numerian and after the assassination of Carinus became sole ruler of the Roman Empire. Diocletian immediately reformed the government of the Roman Empire and in the face of serious military and economic problems established a new form of government called the Tetrarchy. This involved dividing his power over the empire into east and west sectors, he retained control of the East and his colleague Maximian controlled the west. Eight years later, feeling more focus was needed on both civic and military problems, he further the division of power by naming two "Junior Emperors", or Caesari, under each "Senior Emperor", or Augusti. Thus the Tetrarchy, a rule of four, was established and lasted until c. 324.
Alone (??) among Roman emperors, Diocletian retired rather than dying in office - or being murdered, a not-uncommon way to change emperors in the 3rd century. In 305 he retired to his palace on the Adriatic Sea at Split in modern Croatia, not far from Salona, the capital of the Roman province of Dalmatia.