大秦景教流行中国碑
After its split with the West and its adoption of a theology that some called Nestorianism, the Church of the East expanded rapidly in the medieval period due to missionary work. Between 500 and 1400 its geographical horizon extended well beyond its heartland in present-day northern Iraq, northeastern Syria and southeastern Turkey, setting up communities throughout Central Asia and as far as China as witnessed by the Nestorian Stele, a Tang dynasty tablet in Chinese script dating to 781 that documented 150 years of Christian history in China. Their most lasting addition was of the Saint Thomas Christians of the Malabar Coast in India, where they had around 10 million followers.