dioíkēsis

Greek dioíkēsis came from dioikein (to manage a household, to administer), from oikos (house). In the Roman Empire, a diocese was a large administrative district — Emperor Diocletian (reigned 284-305) organized the empire into twelve dioceses, each containing several provinces. The word named a unit of government, not religion. Tax collection, judicial oversight, and military logistics operated at the diocesan level.

As Christianity became the Roman state religion in the fourth century, the Church adopted Roman administrative geography. Bishops' territories mapped onto imperial administrative units. The diocese — a Roman bureaucratic term — became an ecclesiastical one. The bishop managed the diocese as a Roman governor had managed a province. The paperwork changed hands. The word stayed on the desk.

Medieval dioceses varied enormously in size. The Diocese of Rome was small but powerful. The Diocese of York covered most of northern England. Colonial dioceses could span entire continents. The word named territories from a few square miles to hundreds of thousands, unified only by the presence of a bishop. The organizational principle was the same as Diocletian's: divide territory into manageable units with a responsible authority at the head.

Modern Catholic and Anglican churches still use dioceses as their primary administrative unit. There are about 3,100 Catholic dioceses worldwide and approximately 485 Anglican dioceses. Each has a bishop, a cathedral, a chancery, and a bureaucracy. The Roman tax district became a permanent feature of Christian governance. Diocletian would recognize the organizational chart, if not the religion.