, conventionally Irtysh, a river of Siberia and the main left-bank affluent of the Ob [q.v.]. It rises from glaciers on the southern slopes of the Altai mountains near the modern frontier of the Mongolian Republic and Chinese Turkestan or Sinkiang [q.v.] through the Zaysan lake into the Kazakhstan Republic, then out of it into the Omsk oblast of the Russian Federation and joins the Ob at Khanty Mansiysk, its complete course being 3,720 km/2,312 miles, the greater part of it navigable.

The Irtis̲h̲ is mentioned, as ärtis , in the Ork̲h̲on inscriptions (Kültégin E37; Bilgä Kagan E27…