DIOCESE (formed on Fr. diocèse, in place of the Eng. form diocess - current until the 19th century - from Lat. dioecesis, med. Lat. variant diocesis, from Gr., "housekeeping," "administration," , "to keep house," "to govern"), the Sphere of a bishop's jurisdiction. In this, its sole modern sense, the word diocese (dioecesis) has only been regularly used since the 9th century, though isolated instances of such use occur so early as the 3rd, what is now known as a diocese having been till then usually called a parochia (parish). The Greek word , from meaning "administration," came to be applied to the territorial circumscription in which administration was exercised. It was thus first applied e.g. to the three districts of Cibyra, Apamea and Synnada, which were added to Cilicia in Cicero's time (between 56 and 50 b.c.). The word is here equivalent to "assize-districts" (Tyrrell and Purser's edition of Cicero Epist. ad fam. iii. 8. 4; xiii. 67; cf. Strabo xiii. 628-629). But in the reorganization of the empire, begun by Diocletian and completed by Constantine, the word "diocese" acquired a more important meaning, the empire being divided into twelve dioceses, of which the largest - Oriens - embraced sixteen provinces, and the smallest - Britain - four (see Rome: Ancient History; and W. T. Arnold, Roman Provincial Administration, pp. 187, 194-196, which gives a list of the dioceses and their subdivisions). The organization of the Christian church in the Roman empire following very closely the lines of the civil administration (see Church History), the word diocese, in its ecclesiastical sense, was at first applied to the Sphere of jurisdiction, not of a bishop, but of a metropolitan.  Thus Anastasius Bibliothecarius (d. c. 886), in his life of Pope Dionysius, says that he assigned churches to the presbyters, and established dioceses (parochiae) and provinces (dioeceses). The word, however, survived in its general sense of "office" or "administration," and it was even used during the middle ages for "parish" (see Du Cange, Glossarium, s. "Dioecesis" 2).
The practice, under the Roman empire, of making the areas of ecclesiastical administration very exactly coincide with those of the civil administration, was continued in the organization of the church beyond the borders of the empire, and many dioceses to this day preserve the limits of long vanished political divisions. The process is well illustrated in the case of English bishoprics. But this practice was based on convenience, not principle; and the limits of the dioceses, once fixed, did not usually change with the changing political boundaries. Thus Hincmar, archbishop of Reims, complains that not only his metropolitanate (dioecesis) but his bishopric (parochia) is divided between two realms under two kings; and this inconvenient overlapping of jurisdictions remained, in fact, very common in Europe until the readjustments of national boundaries by the territorial settlements of the 19th century. In principle, however, the subdivision of a diocese, in the event of the work becoming too heavy for one bishop, was very early admitted, e.g. by the first council at Lugo in Spain (569), which erected Lugo into a metropolitanate, the consequent division of diocese being confirmed by the king of the second council, held in 572. Another reason for dividing a diocese, and establishing a new see, has been recognized by the church as duly existing "if the sovereign should think fit to endow some principal village or town with the rank and privileges of a city" (Bingham, lib. xvii. c. 5). But there are canons for the punishment of such as might induce the sovereign so to erect any town into a city, solely with the view of becoming bishop thereof. Nor could any diocese be divided without the consent of the primate.
In England an act of parliament is necessary for the creation of new dioceses. In the reign of Henry VIII. six new dioceses were thus created (under an act of 1539); but from that time onward until the 19th century they remained practically unchanged. The Ecclesiastical Commissioners Act 1836, which created two new dioceses (Ripon and Manchester), remodelled the state of the old dioceses by an entirely new adjustment of the revenues and patronage of each see, and also extended or curtailed the parishes and counties in the various jurisdictions.
By the ancient custom of the church the bishop takes his title, not from his diocese, but from his see, i.e. the place where his cathedral is established. Thus the old episcopal titles are all derived from cities. This tradition has been broken, however, by the modern practice of bishops in the United States and the British colonies, e.g. archbishop of the West Indies, bishop of Pennsylvania, Wyoming, etc. (see Bishop).
See Hinschius, Kirchenrecht, ii. 38, etc.; Joseph Bingham, Origines ecclesiasticae, 9 vols. (1840); Du Cange, Glossarium, s. "Dioecesis"; New English Dictionary (Oxford, 1897), s. "Diocese."
 For exceptions see Hinschius ii. p. 39, note 1.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)