The Collaborative International Dictionary
Tetrarchy \Tet"rarch*y\, n.; pl. Tetrarchies. [L. tetrarchia, Gr. ?: cf. F. t['e]trarchie.] (Rom. Antiq.) The district under a Roman tetrarch; the office or jurisdiction of a tetrarch; a tetrarchate.
Wiktionary
n. Historically, an empire that was ruled by four rulers.
Wikipedia
The term tetrarchy (from the Greek τετραρχία "leadership of four [people]") describes any form of government where power is divided among four individuals, but in modern usage usually refers to the system instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire. This tetrarchy lasted until c. 313, when internecine conflict eliminated most of the claimants to power, leaving Constantine in control of the western half of the empire, and Licinius in control of the eastern half.
Usage examples of "tetrarchy".
The distinctive features of the Constantinian empire as compared with that of Diocletian, or of the tetrarchy of which he was the head, were not evolved from earlier political principles, but stood out in bold contrast and even in direct opposition to the very fundamentals of antique statesmanship, and so new in politics that even Constantine permitted them to slip away from his grasp long before the sunset of his life had come.
The man now on the throne of the Galilean and Perean tetrarchy, Herod Antipas, was a son of the notorious Herod the Great, arch-maniac of Jewish legend.
They had fought each other, breaking into pairs and tetrarchies, and meeting here and murdering one another there.
The Drakians opened volley-fire at 400 yards, firing by tetrarchies [platoons].
That was no more than a couple of tetrarchies or the crew of a torpedo gunboat, even if two flag officers commanded it, and all Citizens.