Diocese (διοίκησις, administration), the territorial circuit of a bishop's administration where the Episcopacy is diocesan (q.v.).
1. Roman Civil Dioceses. — The origin of the diocesan division is to be traced to the ancient division of the later Roman empire. The term diocese is used by Cicero (Fam. 3:8, 4) to designate the district of a governor's jurisdiction. Constantine divided the empire into 13 larger divisions, called dioceses, which were again divided into 120 provinces. The dioceses were governed by vicars or prefects. The civil diocesae division in the days of Arcadius and Honorius (beginning of the fifth century) was as follows:
I. Prafectut Pratorio per Orientem: five dioceses were subject to his jurisdiction, namely,
1, the Oriental-diocese, properly so called; 2, the diocese of Egypt; 3, the diocese of Asia; 4, the diocese of Pontus; 5, the diocese of Thrace.
II. Praofectus Praetorio per Illyricum: only two dioceses were committed to his superintendence, namely,
1, the diocese of Macedonia; 2, the diocese of Dacia.
III. Praefectus Praetorio Italiae: three dioceses were subject to the jurisdiction of this governor, namely,
1, the diocese of Italy; 2, the diocese of Illyria; 3, the diocese of Africa.
IV. Praefectus Praetorio Galliarum: he had the command of three dioceses, namely,
1, the diocese of Spain; 2, the diocese of Gaul; 3, the diocese of Britain.
The diocese of Britain included five provinces, namely,
1, Maxima Caesareensis; 2, Valentia; 3, Britannia Prima; 4, Britannia Secunda; 5, Flavia Caesareensis. Or thus:
(Bingham, Orig. Ecclesiastes book 9, chapter 1, where the subject is very fully treated.)
2. Ecclesiastical Dioceses. — "Some suppose the division of a church into dioceses to be the natural consequence of the institution of the office of bishop, and that the rise of the system of diocesan division of a church is to be found in the New Testament. But this is evidently a mistake. In the times of the apostles a diocese and a church appear to have been the same; there was, therefore, no division of any church into dioceses. If it be said that the Church, i.e., the Catholic Church, was thus divided, this too is a mistake. What is divided must have first existed as a whole. Now the Catholic Church never existed as a whole, i.e., as one complete community on earth, from the time that Christianity passed the bounds of Jerusalem. Thenceforward there was not division, but additions of fresh churches" (Eden, Churchman's Dictionary, s.v.). After the order of bishops had fully established itself, and the state had become Christian, the Church took her model of ecclesiastical territorial division from that of the state. About the latter end of the fourth century the Church appears to have been divided in a similar manner with the empire, having an exarch or patriarch in each of the thirteen great dioceses, and a metropolitan or primate in every province. The lesser diocese, used as the word is now, included the episcopal city itself, and all the region round about it, with its numerous congregations under the bishop's jurisdiction; hence it was called the bishop's παροικία, which, in its original application, meant the bishop's whole diocese, though the word parish, or a single congregation, has flowed from it in later days. At a later period the word diocese was transferred to the bishop's field of jurisdiction, and the word patriarchate covered that of the ancient diocese.
In England, up to the twelfth century, bishops were said to exercise their functions within a certain geographical territory called a parish; the word diocese was seldom used, nor was it at all employed in England, with authority from the popes, until A.D. 1138 (Brit. and For. Evang. Review, No. 211, page 223). The Church of England now includes twenty-eight dioceses (including the two archbishoprics); that of Ireland twelve. In the United States a diocese is a territory under the jurisdiction of a single bishop of the Protestant Episcopal or Roman Church, whether comprehending one or more states of the Union, or only part of a state.
New dioceses can be formed in the Protestant Episcopal Church with the consent of the bishop, the Diocesan Convention, and the General Convention. There were in the United States, in 1867, thirty-four dioceses of the Protestant Episcopal Church, and forty-four dioceses of the Roman Catholic Church. In 1868, the pope, in accordance with the proposition made by the "Second Plenary Council of Baltimore," established nine new dioceses, thereby increasing the total number of Roman Catholic dioceses to fifty-three. See Bingham, Orig. Ecclesiastes book 9, chapter 1; Bilson, Perpetual Government of Christ's Church, chapter 14; Hook, Church Dictionary, s.v.; Ferraris, Prompta Bibliotheca, s.v.; Elliott, Delineation of Romanism, book 3, chapter 9; Hooker, Ecclesiastical Polity, book 7, § 8; Siegel, Handbuch der Alterthümer, 4:378.