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's defeat strengthened Tang rule in southern Xinjiang and brought the regions formerly controlled by the khaganate into the Tang empire. The military expedition included 10,000 horsemen supplied by the Uyghurs, who were close allies of the Tang. The Uyghurs had allied with the Tang ever since the dynasty supported their revolt against the reign of the Xueyantuo, a tribe of Tiele people. Xinjiang was administered through the Anxi Protectorate () and the Four Garrisons of Anxi.