The Tetrarchy in Roman history refers to the division of the Roman Empire into a western and eastern empire, with subordinate divisions within the western and eastern empires.
Tetrarchy comes from the Greek words for four (tetra-) and rule (arch-) or what could be called a quadrumvirate (4-man [rule]) if basing it on Latin.
Tetrarchy refers to the establishment by Emperor Diocletian, in 293, of a 4-part division of the Roman Empire. Diocletian continued to rule in the East. He made Maximian his equal and co-emperor in the West. They were each called "Augustus" which signified that they were emperors. Subordinate to them were the two "Caesars": Galerius, in the east, and Constantius in the west. An Augustus was always emperor. Sometimes the Caesars were also referred to as emperors. The reforms of Diocletian came after a period when many emperors had been assassinated. This earlier period is referred to as chaotic and the reforms were meant to remedy the mess that the Roman Empire faced. With 4 men to move through, assassination became less likely, so at least in this sense, this was a more stable form of government.
