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group, headed by the Nestorian patriarch. Although they were not permitted to convert Moslems, Nestorian missionaries were otherwise given a free hand, and by the end of the twelfth century Nestorian churches could be found in Egypt and Cilicia, in Persia and Mesopotamia, in India, Ceylon and Socotra, and in much of Turkestan. All these churches, organised into at least twenty, and possibly as many as thirty, metropolitan provinces, recognised the authority of the Nestorian patriarch or catholicus, who ruled from Baghdad, the capital of the Abbasid caliphate.
The Nestorian church enjoyed a final period of expansion under the Mongols. For a while, during campaigns against Moslem enemies, the Mongols saw that Christian support could be valuable to them, and the Nestorians were able to take advantage of the Mongol unification of Asia from the Euphrates to the Sea of Japan to establish themselves in strength in China in the second half of the thirteenth century. The Nestorian church now reached its greatest geographical extent. But appearances were deceptive. As Mongol power waned throughout Asia the vacuum was filled not by Christianity, but by Islam. The Nestorian church in China did not survive the Mongol Yüan dynasty, and in central Asia most Nestorian Christians apostasised in the face of Moslem persecution in the middle years of the fourteenth century. Any surviving communities of Christians were almost certainly either wiped out or converted to Islam during the terrible campaigns of Timur Leng towards the end of the fourteenth century.
Apart from a tiny offshoot in India, the church which dominated Asia in the middle ages survives today only in Kurdistan, uneasily placed astride the borders of the modern states of Syria, Turkey, Iraq and Iran. Emigration from Kurdistan during the last two centuries has also created a Nestorian diaspora in the United States, Europe, and Australia. The total membership of the Nestorian church was reckoned in 1989 at about 1,770,000.
The Nestorians in China
For more than two hundred years during the T'ang dynasty (618-906), and for a further sixty or seventy years during the Mongol Yüan dynasty (1260-1368), Nestorian Christians could be found in significant numbers in China. The dates are not entirely certain. As far as the T'ang period is concerned, the first officially-recognised Nestorian