The Battle of Irtysh River or Battle of Yexi River was a battle in 657 between Tang Dynasty general Su Dingfang and the Western Turkic Khaganate qaghan Ashina Helu during the Tang campaign against the Western Turks. It was fought along the Irtysh River near the Altai Mountains. Helu's forces, consisting of 100,000 cavalry, were ambushed by Su as Helu chased decoy Tang troops that Su had deployed. Helu was defeated during Su's surprise attack, and lost most of his soldiers. Turkic tribes loyal to Helu surrendered, and the retreating Helu was captured the next day. Helu's defeat ended the Western Turkic Khaganate, strengthened Tang control of Xinjiang, and led to Tang suzerainty over the western Turks