In his accredited work titled Diwan Lughat al-Turk, Mahmud of Kashgar, a Turkic scholar of the 11th century, described the Karachuk Mountains which are located just east of the Aral Sea as the original homeland of the Oghuz Turks. The Karachuk mountains are now known as the Tengri Tagh (Tian Shan in Chinese) Mountains, and they are adjacent to Syr Darya.