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Eparchy is an anglicized Greek word (?), authentically Latinized as eparchia, which can be loosely translated as the rule or jurisdiction over something, such as a province, prefecture, or territory. It has specific meanings both in politics, history and in the hierarchy of the Eastern Christian churches.
In ecclesiastical use, an eparchy is a territorial diocese governed by a bishop of one of the Eastern churches, who holds the title of eparch. It is part of a metropolis. Each eparchy is divided into parishes in the same manner as a diocese of western Christendom. In the Catholic Church, an archieparchy equivalent to an archdiocese of the Roman Rite and its bishop is an archieparch, equivalent to an archbishop of the Roman Rite.
Originally eparchy (?, eparchia) was the Greek equivalent of the Latin term provincia, one of the districts of the Roman Empire. As such it was used, chiefly in the eastern parts of the Empire, to designate the Roman provinces. The term eparch (Greek: ?, eparchos) however, designating an eparchy's governor, was most usually used to refer to the praetorian prefects (singular in Greek: ? ?, "eparch of the praetorium") in charge of the Empire's praetorian prefectures, and to the Eparch of Constantinople, the city's urban prefect.
The Dominate-period administrative system was retained In the Byzantine period of the Empire until the 7th century. As Greek became the Empire's main administrative language, replacing Latin, in the latter 6th century even the provinces of the Exarchate of Ravenna, in reconquered Italy, were termed eparchiae in Greek as well as in Latin.
In the latter half of the 7th century, the old provincial administration was replaced by the thematic system. Even after that however, the term eparchos remained in use until the 840s for the senior administrative official of each thema, under the governing strategos. Thereafter, eparchs are evident in some cases as city governors, but the most important by far amongst them was the Eparch of Constantinople, whose office had wide-ranging powers and functioned continuously until the 13th century.
The term eparchia was revived as one of the administrative sub-provincial units of post-Ottoman independent Greece, the country being divided into nomoi ("Prefectures"), of which in turn some were subdivided into eparchies. From 1887, the eparchies were abolished as actual administrative units, but were retained for some state services, especially finance services and education, as well as for electoral purposes. Before the Second World War, there were 139 eparchies, and after the war, with the addition of the Dodecanese Islands, their number grew to 147. The provinces were abolished in the mainland (but retained for the islands), in the wide-ranging administrative reform implemented in 1997 (the "Kapodistrias plan") and replaced by enlarged municipalities (demoi).
The Christian Church (before the split into Roman Catholic and Eastern Orthodox) adopted elements of political, administrative system of the late Roman Empire, as introduced by the reforms of Diocletian (284-305). Adopted elements included both organizational structure and terminology.
Notwithstanding the primacies of the Apostolic Sees of Rome, Alexandria and Antioch, the bishoprics of each civil province were grouped in one ecclesiastical province, also called eparchy, under the supervision of the metropolitan, usually the bishop of the provincial capital. The First Council of Nicaea in 325 accepted this arrangement and orders that: "the authority [of appointing bishops] shall belong to the metropolitan in each eparchy" (can. iv), i.e., in each such civil eparchy (province) there shall be a metropolitan bishop who has authority over the others.
Since the use of the term eparchy was originally linked to metropolitan rights, later in Eastern Christianity, after a process of title-inflation and multiplying the numbers of metropolitans by elevating local bishops to honorary metropolitan rank without giving them any real metropolitan powers, the use of the word "eparchy" was gradually modified and came to refer to dioceses of such "metropolitan" bishops, and later to dioceses in general. This process was initially promoted in the Ecumenical Patriarchate of Constantinople, and later the new usage of term "eparchy" became prevalent in the Eastern Orthodox Church, the ancient Oriental Churches, and the Eastern Catholic Churches.
In the Eastern Orthodox Church, the name eparchy is not commonly used as the usual term for a diocese except in the Bulgarian, Czechoslovak, Russian, and Serbian Orthodox Churches. The Russian Orthodox Church in the early 20th century counted 86 eparchies, of which three (Kiev, Moscow, and St. Petersburg) were ruled by bishops who always bore the title "Metropolitan."