Ashina Helu
The expansion into Central Asia continued under Taizong's successor, Emperor Gaozong, who invaded the Western Turks ruled by the qaghan Ashina Helu in 657 with an army led by Su Dingfang. Ashina was defeated and the khaganate was absorbed into the Tang empire. The territory 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.