The early Turkic peoples descended from agricultural communities in Northeast Asia who moved westwards into Mongolia in the late 3rd millennium BC, where they adopted a pastoral lifestyle. By the early 1st millennium BC, these peoples had become equestrian nomads. In subsequent centuries, the steppe populations of Central Asia appear to have been progressively replaced and Turkified by East Asian nomadic Turks, moving out of Mongolia. In Central Asia, the earliest surviving Turkic-language texts, found on the eighth-century Orkhon inscription monuments, were erected by the Göktürks in the sixth century CE, and include words not common to Turkic but found in unrelated Inner Asian languages. Although the ancient Turks were nomadic, they traded wool, leather, carpets, and horses for wood, silk, vegetables and grain, as well as having large ironworking stations in the south of the Altai Mountains during the 600s CE. Most of the Turkic peoples were followers of Tengrism, sharing the cult of the sky god Tengri, although there were also adherents of Manichaeism, Nestorian Christianity and Buddhism. However, during the Muslim conquests, the Turks entered the Muslim world proper as slaves, the booty of Arab raids and conquests. The Turks began converting to Islam after the Muslim conquest of Transoxiana through the efforts of missionaries, Sufis, and merchants. Although initiated by the Arabs, the conversion of the Turks to Islam was filtered through Persian and Central Asian culture. Under the Umayyads, most were domestic servants, whilst under the Abbasid Caliphate, increasing numbers were trained as soldiers. By the ninth century, Turkish commanders were leading the caliphs’ Turkish troops into battle. As the Abbasid Caliphate declined, Turkish officers assumed more military and political power by taking over or establishing provincial dynasties with their own corps of Turkish troops.