Ashina Helu
The expansion into Central Asia continued under Taizong's successor, Emperor Gaozong, who dispatched an army in 657 led by Su Dingfang against the Western Turk qaghan Ashina Helu. Ashina was defeated and the khaganate was absorbed into the Tang empire. The Tarim Basin was administered through the Anxi Protectorate and the Four Garrisons of Anxi. Tang hegemony beyond the Pamir Mountains in modern Tajikistan and Afghanistan ended with revolts by the Turks, but the Tang retained a military presence in Xinjiang. These holdings were later invaded by the Tibetan Empire to the south in 670. For the remainder of the Tang Dynasty, the Tarim Basin alternated between Tang and Tibetan rule as they competed for control of Central Asia.