A History of Christianity: The First Three Thousand Years

by Diarmaid MacCulloch

Significantly, imperial Christianity came to follow the political division of the empire which had originally been established by its archenemy Diocletian, when he split the administration of his empire between east and west, with a dividing line running through central Europe to the west of the Balkans, and a separation of North Africa and Egypt. In Europe, that boundary is very largely that existing today between Orthodox and Catholic societies, with fairly minor adjustments, even to the division of Slavic peoples between Orthodoxy and Catholicism. Moreover, the Church started using a technical administrative term which Diocletian had adopted for the twelve subdivisions he created in the empire: ‘diocese’. In the Western Latin Church, this has become the term for an area under the control of a bishop.