Bogu Khagan

Manichaeism was persecuted almost everywhere it went. It was proscribed in the Roman empire, hunted in Sasanian Persia where it began, and periodically suppressed in China. The Uyghur Khaganate on the Mongolian steppe is the single exception: for something over seventy years from the 760s, the religion of Mani was the religion of a state.

The decision belongs to Bogu Khagan. He had taken Uyghur forces into China to help the Tang court recover from the rebellion of An Lushan, and at Luoyang in the early 760s he encountered Manichaean teachers, most of them Sogdians from the trading network that ran along the routes through Central Asia. He took several of them back with him and made the religion official.

The practical consequences were considerable. Manichaeism required its elect to abstain from meat and from agricultural labour, which is not an obvious fit for a nomadic economy, and their support fell on the hearers. The Sogdian merchants who carried the religion also carried literacy, and the Uyghurs took up a script derived from Sogdian that later passed to the Mongols. When the khaganate fell in 840 and the Uyghurs moved south-west into the Tarim basin, the religion went with them, and it is the Turfan oasis that has since yielded most of the Manichaean literature surviving anywhere in the world.

The main source is a stele at Karabalgasun, the Uyghur capital in the Orkhon valley, inscribed in three languages: Chinese, Sogdian and Old Turkic. All three faces are damaged and no single face preserves the whole account, so the conversion has to be reconstructed by fitting fragments together. The Chinese face is the best preserved and presents the change as the khagan being instructed by teachers of the religion of light; the Sogdian face supplies detail the Chinese does not.

Chinese dynastic histories add an outside view and they are not friendly. The Tang record notes the Manichaean temples permitted in Chinese cities at Uyghur insistence and treats them as a concession extracted by a difficult ally, and it associates the religion with Sogdian merchants whose dealings the court resented.

Bogu Khagan was killed in 779 by his cousin Tun Bagha Tarkan, in a coup the Chinese sources connect to a plan to invade China that the Uyghur nobility did not want. Manichaeism survived the man who imposed it, which is the strongest evidence that it had taken root beyond the court, and later khagans went on patronising it. Reconstructing the episode means reading a damaged trilingual monument, a hostile foreign chronicle and later religious manuscripts from Turfan against one another, which is the ordinary condition of steppe religious history rather than a special difficulty here.