Nestorius was a fifth-century Patriarch of Constantinople, deposed and driven into exile for having preached heretical Christology, reportedly maintaining (though Nestorius himself denied it) that the Logos lived in the person of Jesus, who would thus be the bearer of God, and not the man-God, the orthodox position, two natures in one substance. Surprisingly, the decision to anathematize Nestorius turned out to have interesting consequences in Central Asian history, and perceptions of Central Asia in medieval Europe.
The Persian church had been autonomous from 410, possessing its own Patriarch, independant of the authority of the Western churches, and in 486 made a decision to uphold Nestorius’s teachings, in part to distinguish themselves from the West and reduce the chance that Persian Christians would gravitate to Antioch and Constantinople; non-Nestorians were driven from the country (though the Armenians condemned the move). Symmetrically, Nestorians fled Western areas to Persia, just as three hundred years earlier Christians had fled the then-pagan Roman Empire to take refuge with the Persian church.
By the middle of the sixth century, Nestorians churches had sprung up all over Asia, from Sri Lanka to Mongolia and from Egypt to China, and everywhere in between, including Turkestan, India, Afghanistan, and Kyrgyzstan. Like many missionaries confronted with illiterate societies, the Nestorians were led to create writing systems for the languages of peoples they wished to convert, such as Mongolian, Uighur, Sogdian, and Manchu, all based on Syriac.