Dioceses of the Church of the East to 1318

At the height of its power, in the 10th century AD, the dioceses of the Church of the East numbered well over a hundred and stretched from Egypt to China. These dioceses were organised into six interior provinces in Mesopotamia, in the Church's Iraqi heartland, and a dozen or more second-rank exterior provinces. Most of the exterior provinces were located in Iran, Central Asia, India and China, testifying to the Church's remarkable eastern expansion in the Middle Ages. A number of East Syrian dioceses were also established in the towns of the eastern Mediterranean, in Palestine, Syria, Cilicia and Egypt.

There are few sources for the ecclesiastical organisation of the Church of the East before the Sassanian (Persian) period, and the information provided in martyr acts and local histories such as the Chronicle of Erbil may not always be genuine. The Chronicle of Erbil, for example, provides a list of East Syrian dioceses supposedly in existence by 225. References to bishops in other sources confirm the existence of many of these dioceses, but it is impossible to be sure that all of them had been founded at this early period. Diocesan history was a subject particularly susceptible to later alteration, as bishops sought to gain prestige by exaggerating the antiquity of their dioceses, and such evidence for an early diocesan structure in the Church of the East must be treated with great caution. Firmer ground is only reached with the 4th-century narratives of the martyrdoms of bishops during the persecution of Shapur II, which name several bishops and dioceses in Mesopotamia and elsewhere.

The ecclesiastical organisation of the Church of the East in the Sassanian period, at least in the interior provinces and from the 5th century onwards, is known in some detail from the records of synods convened by the patriarchs Isaac in 410, Yahballaha I in 420, Dadishoʿ in 424, Acacius in 486, Babaï in 497, Aba I in 540 and 544, Joseph in 554, Ezekiel in 576, Ishoʿyahb I in 585 and Gregory in 605. These documents record the names of the bishops who were either present at these gatherings, or who adhered to their acts by proxy or later signature. These synods also dealt with diocesan discipline, and throw interesting light on the problems which the leaders of the church faced in trying to maintain high standards of conduct among their widely dispersed episcopate.

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Wikipedia