"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...."
Read all about it in The Argus: Nestorians and the Legend of Prester John