An exarch, from the Greek ἔξαρχος (exarchos), was the title given to a governor of the Eastern Roman (Byzantine) Empire who had extended authority in a province that was distant from the capital, Constantinople. The title came to be applied to a bishop of the Orthodox Church who was a deputy of a patriarch, a bishop who has authority over other bishops without being a patriarch, or a bishop who is appointed to lead a group of people that is not large or organized enough to be constituted an diocese/eparchy.
In 476, after the fall of the Roman Empire in the West, the Eastern Roman Empire remained stable through the early years of the Middle Ages and retained the ability for expansion. During this period Emperor Justinian re-conquered, as part of the Eastern Roman Empire, North Africa, Italy, Dalmatia, and parts of Spain. This expansion put an incredible strain on the limited resources of the Empire, but later emperors would not surrender the re-conquered lands to remedy the strain on resources. This set the stage for establishment of the Exarchates to handle locally the constantly evolving situation in the provinces.
The Exarchates were a response to weakening imperial authority in the provinces, particularly in Italy and North Africa, and were part of the overall process of unification of civil and military offices in these lands. This type of organization initiated in an early form by Justinian led eventually to the creation of the Theme system by emperor Heraclius. The first exarchate, with [Ravenna]] at its center, was formed and organized during the reign of Emperor Maurice. The exarch functioned also as the representative of the Patriarch of Constantinople. Similarly, separate exarchates were established for Byzantine Sicily and Africa. By the mid eighth century all these exarchates were lost under the advance of the Lombards and Franks.
The term exarch first entered the ecclesiastical language as a title for a metropolitan with jurisdiction not only for the area for which he was a metropolitan, but also over other metropolitans. The First Ecumenical Council (held in 451), which gave special authority to the see of Constantinople as being "the residence of the emperor and the Senate," did not use the term "patriarch", but in its ninth canon still spoke only of "exarchs".
The title patriarch came about when the Imperial government proposed an organization for a universal Christendom that was composed of five patriarchal sees (Rome, Constantinople, Alexandria, Antioch, and Jerusalem, known as the pentarchy). This was done under the auspices of a single universal empire as formulated in the legislation of Emperor Justinian, especially in his Novella 131. Having received formal ecclesiastical sanction at the Council of Trullo (held in 692), the name "patriarch" became the official title for the Bishops of these sees. The title "Exarch" remained the proper style for metropolitans who ruled over the three remaining (political) dioceses of Diocletian's division of the Eastern Prefecture. These were the Exarchs of Asia (at Ephesus), of Cappadocia and Pontus (at Caesarea), and of Thrace (at Heraclea Sintica). Later the advance of the stature of Constantinople put an end to these exarchates, and they fell back to the state of ordinary metropolitan sees (Fortescue, Orthodox Eastern Church, 21-25). But the title of exarch was still occasionally used for any Metropolitan (so at Sardica in 343, can. vi).
The principle was established that, since no addition should be made to the fixed number of five patriarchs of the pentarchy, any bishop with authority over other bishops who was not dependent on any one of these five should be called an exarch. Thus, since the Church of Cyprus was declared autocephalous (at Ephesus in 431), its Primate received the title of Exarch of Cyprus.
The short-lived medieval Churches of Ipek (for Serbia), Achrida (for Bulgaria) and Tirnova (for Romania), were governed by exarchs, though these prelates occasionally assumed the title of patriarch (Fortescue, Orthodox Eastern Church, 305 sq. 317 sq., 328 sq.). On the same principle the Archbishop of Mount Sinai is an exarch, though in this case, as in that of Cyprus, modern Orthodox usage generally prefers the title "Archbishop".
On February 28, 1870, the twenty-year old struggle between Greeks and Bulgarians for the control of the Church in Bulgaria culminated when the Ottoman Sultan Abd-ul-Aziz created an independent Bulgarian ecclesiastical organization, known as the Bulgarian Exarchate, with its head given the title of Exarch, not that of Patriarch. The Church of Bulgaria had then become independent of the Greek-dominated Patriarchate of Constantinople. The Bulgarian Exarch resided at Constantinople, the Ottoman capital.
The head of the Church of Georgia, which had been autocephalous since 750, was styled, since 1008, as Catholicos-Patriarchs of Iberia, i.e. the Caucacus. In 1802, after imperial Russia destroyed the independence of the Georgian Church, the Primate of Georgia (who was always a Russian) sat in the Holy Synod at St. Petersburg with the title of Exarch of Georgia (Fortescue, Orthodox Eastern Church, 304-305). On April 7, 1917 the Georgian Patriarchate was restored with the title of Catholicos-Patriarch of All Georgia. Its autocephaly was recognized by the Church of Russia, in 1943, and by the Constantinople Patriarchate on March 3, 1990.
Today in the Orthodox Church, an Exarch is usually a deputy of a Patriarch. In many cases he rules, on behalf of the Patriarch, a Church outside the home territory of the Patriarchate. Thus, in the United States of America, there are Exarchs representing, among others, the Serbian, Romanian, Bulgarian and Jerusalem Patriarchs. The style of the Exarchs of the Patriarchate of Jerusalem is "Exarch of the Holy Sepulcher".
In 1972, Bishop Jose and the Mexican National Church were accepted by the Orthodox Church in America as the "Exarchate of Mexico (OCA)|Exarchate of Mexico]]," with Archbishop Dmitri (Royster) of Dallas|Dimitri of Dallas]] and the South serving as Exarch of Mexico in addition to his responsibilities for the Diocese of the South.
The Oriental Orthodox Patriarch of Antioch has under his authority an Exarch in India, known by the ancient title Maphrian, although he is popularly referred to as Catholicos. This is not to be confused with the autocephalous Catholicate of the East, which is also located in India.