Under intense political pressure from the Sasanian Empire, the Persian church declared its independence from the Roman Church in 424 CE. Four years later Nestorius was appointed patriarch of Constantinople and soon provoked a doctrinal storm by challenging the established church position that Mary was a theotokos (God-bearer), declaring that Christ’s two natures (divine and human) meant he should be seen as having two persons, the divine Word and the fully human Jesus. In 431 CE at the first council of Ephesus, these positions were anathematised, and Nestorius was deposed and exiled. The resulting schisms saw many of his supporters fleeing to Sasanian territory, and on the principle that and “enemy’s enemy is one’s friend” the ruling class and encouraged Nestorianism in its Christian communities. Nestorian missionaries travelled far and wide. They journeyed down the Arabian peninsula to Yemen and exported their beliefs along the silk Road to distant China. The Mongols had been proselytised since the 7th century and a substantial minority, some of them very powerful warlords, were Nestorian Christians.
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