In the period of its greatest expansion, in the tenth century, the Syriac Orthodox Church had around 20 metropolitan dioceses and a little over a hundred suffragan dioceses. By the seventeenth century, only 20 dioceses remained, reduced in the twentieth century to 10. The seat of Syriac Orthodox Patriarch of Antioch was at Mardin before the First World War, and thereafter in Deir Zaʿfaran, from 1932 in Homs, and finally from 1959 in Damascus.

Syriac Orthodox Church before the Arab invasions When the Syriac Orthodox movement began in the sixth century, the Christian world was organised into five patriarchates: Rome, Constantinople, Antioch, Alexandria and Jerusalem. The Syriac Orthodox movement was initially confined to the eastern provinces of the Roman Empire, in the territory of the patriarchates of Antioch and Jerusalem. Syriac Orthodox Christians envisaged their church as the legitimate patriarchate of Antioch from the line continuing from Severus of Antioch.

Syriac Orthodox Church under the caliphate

Over a hundred Syriac Orthodox dioceses and around a thousand bishops are attested between the sixth and thirteenth centuries. The main sources for these dioceses and bishops are the lists of Michael the Syrian, compiled in the twelfth century. Many other dioceses and bishops are mentioned in other literary sources, particularly the works of Bar Hebraeus, written in the second half of the thirteenth century. Several bishops not known either to Michael the Syrian or Bar Hebraeus are mentioned in the colophons of surviving West Syriac manuscripts.

Syria Eight Syriac Orthodox dioceses are known to have existed at various periods before the fourteenth century in southern Syria, in the areas covered by the Chalcedonian province of Phoenicia Libanesia and the southern part of the province of Euphratensis. There was a Syriac Orthodox diocese for Damascus, first attested in the seventh century. The diocese persisted into the fourteenth century and appears to have been one of the few Syriac Orthodox dioceses which continued undisturbed into the fifteenth century and beyond. Emesa (Homs) and Palmyra (Tadmor) also had Syriac Orthodox dioceses. (Emesa) and 251 (Palmyra) There was an ephemeral Jacobite diocese for the coastal port of Laodicea (Latakia) in the ninth century; and an ephemeral Jacobite diocese for Sadad, a town between Damascus and Homs, in the twelfth century.

There was also a Syriac Orthodox diocese for Heliopolis (Baalbek), attested between the seventh and eleventh centuries; and a diocese for Kfar Tab near Homs, attested in the eleventh and twelfth centuries. No record has survived of Syriac Orthodox bishops in the other towns in Phoenicia Libanesia with known Chalcedonian dioceses (Salamias, Evaria, Iabruda, Abila and Chonochora), though Iabruda certainly had a Syriac Orthodox community. As far as the southern part of the Chalcedonian province of Euphratensis is concerned, a Syriac Orthodox diocese is attested for Sergiopolis (Resafa) in the ninth and tenth centuries.

Nine Syriac Orthodox dioceses are known to have existed at various periods before the fourteenth century in northern Syria. The diocese of Apamea, which was the seat of a metropolitan by the eighth century, is attested between the seventh and tenth centuries; Seleucia Pieria in the eighth and ninth centuries; Berrhoea (Aleppo) between the seventh and late-thirteenth centuries; Beth Balesh between the eighth and eleventh centuries; Cyrrhus between the eighth and eleventh centuries; Qenneshrin between the eighth and tenth centuries; Mabbugh between the ninth and twelfth centuries; Gishra between the eighth and tenth centuries; and Karshena (Gudpaï) in the eleventh and twelfth centuries.

The diocese of Gishra was incorporated into the diocese of Mabbugh during the reign of Athanasius IV (987–1003), and Mabbugh in turn was incorporated into the diocese of Marʿash in the Commagene district in 1155. It is unlikely that any of these dioceses, with the possible exception of Aleppo, persisted beyond the early years of the fourteenth century. Although an almost unbroken succession of bishops of Aleppo is attested from the early years of the sixteenth century onwards, no fourteenth- or fifteenth-century bishops of Aleppo are known. It seems likely that the diocese of Aleppo lapsed after the death of its bishop Mikha'il, attested in 1298, and was only revived at the beginning of the sixteenth century.

Palestine

There were two stable Syriac Orthodox dioceses in Palestine between the Eighth and Twelfth Centuries, one for the Golan region (whose bishops sat first at Paneas and later at Tiberias) and the other for Jerusalem. The Syriac Orthodox bishops of Golan resided at Paneas, the classical city of Caesarea Philippi, during the seventh and eighth centuries; and at Tiberias in the ninth, tenth and eleventh centuries. Jerusalem was the seat of a Syriac Orthodox bishop at least as early as the eighth century. For most of the period covered by the lists of Michael the Syrian, both dioceses had metropolitan bishops. The diocese of Tiberias lapsed in the twelfth century but the diocese of Jerusalem, whose bishops may have resided in Tripolis for several decades after the recapture of Jerusalem by the Moslems in 1240, seems to have persisted into the fourteenth century. A short-lived Syriac Orthodox diocese of ʿAkko was also established in the Crusader stronghold of Acre in the thirteenth century, which doubtless lapsed after the fall of Acre to the Mamluks in 1291.

Cilicia Eleven separate Syriac Orthodox dioceses are attested at various periods in Cilicia, the most important of which seem to have been Tarsus, Adana and Anazarbus. Tarsus, the metropolis of the Chalcedonian province of Cilicia Prima, is first mentioned as a Syriac Orthodox diocese in the seventh century, and survived as the seat of a Syriac Orthodox bishop or metropolitan until the end of the thirteenth century, the only Cilician diocese which appears to have persisted for so long. Syriac Orthodox bishops, and later metropolitans, of both Adana and Anazarbus are attested between the seventh and twelfth centuries. Other Syriac Orthodox dioceses attested between the seventh and tenth centuries include Citidiopolis (seventh century), Hamam (ninth to twelfth centuries), Hanzit (ninth century), Kinisa (ninth century) and Irenopolis (ninth and tenth centuries).

As a frontier province of the Roman empire, Cilicia was affected by the varying fortunes of war, and three later dioceses reflected Christian successes against the Arabs. Part of Cilicia was settled by Syriac Orthodox Christians in the tenth century, and a diocese of Gihon, created at this period, persisted into the twelfth century. Its bishops sat in the Monastery of Bārid, and the diocese is sometimes referred to as 'Gihon and Barid'. A Syriac Orthodox diocese of Kalinag, in eastern Cilicia, is attested in the eleventh century. A Syriac Orthodox diocese for Sis, then under Armenian rule, was established in the second half of the thirteenth century, whose bishops normally resided in the monastery of Gawikath. One of the bishops of Sis claimed the title of patriarch around the end of the thirteenth century and founded a line of patriarchs which persisted into the fifteenth century.

Cappadocia Seventeen Syriac Orthodox dioceses are known to have existed at various periods before the fourteenth century in Cappadocia. The diocese of Melitene, which seems to have been the seat of a metropolitan from the late ninth century onwards, is attested between the seventh and thirteenth centuries; Simandu (also the seat of a metropolitan) between the tenth and twelfth centuries; Zuptara between the eighth and eleventh centuries; Gubos and Qlisura between the ninth and thirteenth centuries; ʿArqa, Gargar, Laqabin and Qlaudia between the tenth and thirteenth centuries; Tel Patriq in the eleventh and twelfth centuries; Hisn Mansur, Hisn Ziyad (Harput) and Semha between the eleventh and thirteenth centuries; Caesarea in Cappadocia in the twelfth and thirteenth centuries; and Guma in the thirteenth century. There were also ephemeral dioceses for Arabissus around the end of the tenth century and for Romana in the twelfth century. It is doubtful whether any of these dioceses, with the possible exceptions of Gargar and Hisn Ziyad, persisted into the fourteenth century. The dioceses of Gargar and Hisn Ziyad are again attested from the late fourteenth and mid-fifteenth century respectively, but may have been revived, as no bishops of either diocese are known for more than a century before they are again mentioned.

Commagene Nine Syriac Orthodox dioceses are known to have existed before the fourteenth century in the Commagene district. The diocese of Samosata, which appears to have been the seat of a metropolitan from the late eighth century onwards, is attested between the sixth and twelfth centuries; Germanicea (Marʿash) between the seventh and twelfth centuries; Urim between the eighth and ninth centuries; Dolikh between the ninth and eleventh centuries; Hadath between the eighth and eleventh centuries; Kaisum between the eighth and twelfth centuries; Zeugma between the ninth and twelfth centuries; Raʿban between the eleventh and thirteenth centuries; and Tel Bshir (an ephemeral diocese in Crusader territory) in the twelfth century. It is doubtful whether any of these dioceses persisted into the fourteenth century.

Osrhoene

Seven Syriac Orthodox dioceses are known to have existed in Osrhoene before the fourteenth century: the metropolitan diocese of Edessa, attested between the seventh and fourteenth centuries; Callinicus (Raqqa), which also became the seat of a metropolitan in the ninth century, between the eighth and thirteenth centuries; Sarugh (Batna) between the eighth and twelfth centuries; Harran between the seventh and thirteenth centuries; Sibaberek (Severek) in the twelfth century; Khabur between the eighth and thirteenth centuries; and Tella d'Mauzalath (ancient Constantina, modern Viransehir) between the seventh and tenth centuries. None of these dioceses seem to have survived into the fourteenth century.

Amid Four substantial Syriac Orthodox dioceses are known to have existed before the fourteenth century in the Amid region: the dioceses of Amid and Maiperqat, attested between the seventh and thirteenth centuries; the diocese of Arsamosata, attested between the ninth and twelfth centuries; and the diocese of Hattakh, first mentioned towards the end of the thirteenth century. Bar Hebraeus also mentions a bishop of Aspharin, an ephemeral diocese carved out of the diocese of Amid by the patriarch Iwanis I (740–55), which existed for only a few years in the middle of the eighth century.Bar Hebraeus, Chronicon Ecclesiasticum (ed. Abeloos and Lamy), i. 310; The dioceses of Amid and Maiperqat persisted into the fourteenth century. The diocese of Hattakh, first mentioned in 1293, is not again mentioned until 1479, and it is not clear whether it survived into the fourteenth century or was later revived.

Arzun The Arzun region had three stable Syriac Orthodox dioceses before the fourteenth century: Arzun, attested between the seventh and twelfth centuries; Armenia (Akhlat), attested between the ninth and eleventh centuries; and Hesna d’Kifa, first attested in the eighth century. A short-lived diocese was also established at the end of the eighth century for Qalinqala (ancient Theodosiopolis, modern Erzerum), 'a city of Armenia'.Michael the Syrian, Chronicle, iii. 451; Wastan, a city on the shore of Lake Van, was also a Jacobite diocese in the second half of the tenth century, but does not seem to have persisted into the eleventh century.

Mardin