The Eurasian steppe, the vast grassland corridor running from Mongolia across Kazakhstan toward the Black Sea, was the homeland of the horse-riding Turkic and Mongolic peoples, and it gave the world one of its most durable indigenous religions: Tengrism, the worship of the eternal blue sky. Unlike many ancient religions known only through later or foreign sources, Tengrism is directly attested in the peoples' own words: the eighth-century Orkhon inscriptions, carved in the Old Turkic script on great stone steles for the Kok Turk rulers, open by invoking Tengri, the sky god, and describe the khagan as ruling by his mandate, "when the blue sky above and the brown earth below were created, between the two were created the sons of men."
The religion centred on Tengri and on Yer-Su (earth-water spirits) and the goddess Umay, protector of childbirth, and it sanctioned the authority of the khagan as sky-appointed. This sky-mandate ideology reached its widest influence under the Mongol empire of Chinggis Khan, whose conquests were understood as the will of Eternal Heaven. The steppe was also a great conduit of other faiths, Buddhism, Manichaeism, Nestorian Christianity, and eventually Islam all travelled and took root along its routes, so that the region functioned both as the home of an indigenous sky-religion and as a highway over which the world religions crossed Asia.