Uighurs, a historical Turki people, who towards the close of the 10th century rose to great power under the Khan, Satuk Boghra. Bishbalik, the present Urumtsi, was the chief seat of their empire, which stretched from the frontiers of China to the Caspian Sea. Before the introduction of Islam under Satuk Boghra the Uighurs had been converted in large numbers to Christianity by missionaries from Syria, who first arrived in the seventh century, and reduced the Uiguric language to written form with an alphabet based on the Syriac. This script was afterwards adopted by the Mongolians and Manchus, amongst whom it is still in use. The Uighurs, who are the Hoei-Hoei and Kas-che of the Chinese records, are extinct as a separate nationality; but, having taken part in the first Mongol invasion of Europe, their name still survives in the "ogres" of fable and the nursery. The Chentu people of the Turfan district, south-east of Urumtsi, claimed to be descendents of the Uighurs, and in 1892 Russian explorer,Grum-Grijimailo, discovered in their territory many remains of the former Uighur culture.