Tetrarchy

The Tetrarchy was a system of government created by the Roman Emperor Diocletian in order to solve serious military and economic problems in the Roman Empire. 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 furthered the division of power by naming one "Junior Emperor", or Caesar, under each "Senior Emperor", or Augustus. Thus the Tetrarchy, a rule of four, was established and lasted until c. 324.

Constantine I's father Constantius Chlorus was appointed a Caesar in the Tetrarchy in 293.