Central Asia is the belt of oasis cities and mountain passes between Persia, China and the steppe, and almost every religion of the Old World passed through it.
Buddhism went east along these roads. Monasteries in Bactria and the Tarim basin housed the translators who carried Indian texts into Chinese, and the pilgrim Xuanzang travelled the same route westward in the seventh century and left a detailed account of what he found in each kingdom. The colossal buddhas cut into the cliff at Bamiyan, destroyed in 2001, belonged to that world.
Manichaeism spread from Mesopotamia along the same corridor, was adopted as the state religion of the Uyghur steppe empire in the eighth century, and survived longest in Chinese Central Asia; a great deal of what is known about it comes from manuscripts recovered from Turfan, in several languages and scripts. The Church of the East ran bishoprics along the route and reached China by the seventh century. Zoroastrian communities were established throughout, and Sogdian merchants carried all of these traditions as part of their trading networks.
After the Arab conquests the region became one of Islam's great centres of learning. Bukhara and Samarkand produced hadith collectors, jurists and philosophers whose work is standard across the Muslim world, and the Naqshbandi Sufi order, which became one of the most widespread anywhere, began at Bukhara in the fourteenth century.