The Sayan Mountains (Russian: Саяны; Mongolian: Соёны нуруу, Sayany/Soyony nuruu; Kogmen Mountains during the period of the Göktürks) are a mountain range in southern Siberia, Russia and northern Mongolia. In the past, it used to serve as the border between Mongolia and Russia.The Eastern Sayan extends 1,000 km (621 mi) from the Yenisei River at 92° E to the southwest end of Lake Baikal at 106° E.