A stone slab set up in 781 and rediscovered in the seventeenth century records, in Chinese with Syriac names down the side, that a missionary named Alopen reached Chang'an in 635, that his scriptures were translated and examined at imperial order, and that a decree permitted the teaching to be practised. The Church of the East called itself the luminous religion in Chinese, and the stele is the single most important document of Christianity's first arrival in China, describing doctrine in vocabulary borrowed from Buddhism and Taoism because no other vocabulary existed.
It was not alone. Manichaeans obtained official recognition in the Tang capital, largely through the Uighur allies who had adopted the religion; Zoroastrian fire temples served the Sogdian merchant communities; and Muslim traders were present from early in the dynasty, with the Great Mosque of the city traditionally dated to this period. Chang'an at its height was probably the most religiously mixed city on earth.
That ended abruptly. In 845 the emperor Wuzong, a Taoist by conviction and a treasury by necessity, ordered the suppression of Buddhism: thousands of monasteries were closed, hundreds of thousands of monks and nuns returned to lay life, bronze images were melted for coin, and monastic land was confiscated. The foreign religions were swept up in the same edicts. Chinese Buddhism recovered, though the scholastic schools never regained their position. The Church of the East, Manichaeism and Zoroastrianism in China effectively did not.