Book of Zhou
Contemporary Chinese sources conflict as to whether the Turks had a written language by the 6th century. The "Book of Zhou", dating to the 7th century, mentions that the Turks had a written language similar to that of the Sogdians. Two other sources, the "Book of Sui" and the "History of the Northern Dynasties" claim that the Turks did not have a written language. According to István Vásáry, Old Turkic script was invented under the rule of the first khagans and that it was modelled after the Sogdian fashion. Several variants of the script came into being as early as the first half of the 6th century.