The Battle of the Defile or Battle of the Pass () was fought in the Takhtakaracha Pass (in modern Uzbekistan) between a large army of the Umayyad Caliphate and the Turkic Türgesh khaganate over three days in July 731 CE. The Türgesh had been besieging Samarkand, and Samarkand's commander, Sawra ibn al-Hurr al-Abani, had sent a request for relief to the newly appointed governor of Khurasan, Junayd ibn Abd al-Rahman al-Murri. Junayd's 28,000-strong army was attacked by the Türgesh in the pass, and although the Umayyad army managed to extricate itself and reach Samarkand, it suffered enormous casualties; Sawra's 12,000 men, who had been commanded to attack the Türgesh from the rear in a relief effort, were almost annihilated. The battle, for which one of the most detailed accounts of the entire Umayyad era survives in the History of al-Tabari, halted or reversed Muslim expansion into Central Asia for a decade. The losses suffered by the Khurasani army also led to the transfer of reinforcements from the metropolitan regions of the Caliphate, which in the long term weakened the Umayyad regime and helped bring about its collapse twenty years later in the Abbasid Revolution that began in Khurasan. Background The region of Transoxiana had been conquered by the Muslim Arabs of the Syria-based Umayyad Caliphate under Qutayba ibn Muslim in the reign of al-Walid I (), following the Muslim conquest of Persia and of Khurasan in the mid-7th century. The loyalties of the region's native Iranian and Turkic inhabitants and autonomous local rulers remained volatile, and in 719, they sent a petition to the Chinese and their vassals the Türgesh (a Turkic tribal confederation) for military aid against the Muslims. In response, Türgesh attacks began in 720, and the native Sogdians launched uprisings against the Caliphate. These were suppressed with great brutality by the governor of Khurasan, Sa'id ibn Amr al-Harashi, but in 724 his successor, Muslim ibn Sa'id al-Kilabi, suffered a major disaster (the so-called "Day of Thirst") while trying to capture Ferghana. For the next few years, Umayyad forces were limited to the defensive. Efforts to placate and win the support of the local population by abolishing taxation of the native converts to Islam () were undertaken, but these were half-hearted and soon reversed, while heavy-handed Arab actions further alienated the local elites. In 728 a large-scale uprising, coupled with a Türgesh invasion, led to the abandonment of