In A.D. 635, the church in Western Europe was just settling into the feudal Middle Ages, and in Eastern Europe, Christianity was flourishing in the midst of the great Byzantine era. Further east, the Nestorian Church, based in Syria and Persia, was looking to China. That year it sent missionaries to walk via the silk trade route to China's northwest to spread the faith. The first missionaries to China, then, were considered heretical.
Since the 400s, Nestorians had been theological castoffs because they believed Jesus' nature consisted of two persons (rather than one person with two natures). After being condemned at the Council of Chalcedon (451), Nestorians moved east. They retained their missionary zeal and sent representatives to evangelize Arabia and India.
In China, the Nestorian bishop, Alopen, was welcomed to Chang-An (now Xi'an) by the reigning emperor, T'ang T'ai Tsung. In the cosmopolitan atmosphere of the Chinese capital, the emperor granted the newcomers space in the imperial library to translate. He himself studied the faith and gave orders for its propagation. Within a few decades, the Nestorian faith gained thousands of converts in several major cities, though its greatest growth may have been among foreigners trading in China.
Two centuries later, though, Emperor Wu Tsung began a severe persecution, and soon the Nestorian church lost its foothold in China proper (though not on the northern frontier).
Khubilai Khan's curiosity
In the late 1200s, Khubilai Khan, Mongol ruler of China, met representatives of Roman Catholicism: Marco Polo and his uncles. Khubilai Khan was so intrigued, he sent the uncles back to Rome with an invitation for the pope to send 100 "teachers of science and religion" who would try to prove ...