The Battle of Talas(怛羅斯會戰) in 751 AD was a conflict between the Arab Abbasid Caliphate and the Chinese Tang Dynasty for control of the Syr Darya. On July 751, The Abbasides started a massive attack against the Chinese on the banks of the Talas river; 200,000 Muslim troops met the combined army of 10,000 Tang Chinese and 20,000 Karluks mercenary. Although the Chinese cavalry seemed to initially overwhelm the Arab cavalry, the Arab army was larger and the battle dragged on for five days. The tide of the battle turned when Karluks mercenaries betrayed the Tang troops and attacked it from the rear. Out of 10,000 Tang troops, only 2000 managed to return from Talas to their territory in Central Asia.
The defeat was due to the defection of Karluk mercenaries and the retreat of Ferghana allies who originally supported the Chinese. The Karluks forces, which composed of two third of the Tang army, deserted the Chinese coalition and changed to the Muslim side while the battle was ongoing. With the Karluk troops attacking the Tang army from the rear and the Arab attacking from the front, the Tang troops were unable to hold their positions. The commander of the Tang forces, Gao Xianzhi, recognized that defeat was imminent and managed to escape with some of his Tang regulars with the help of Li Siye. Despite losing the battle, Li did inflict heavy losses on the pursuing Arab army after being reproached by Duan Xiushi. After the battle, Gao was prepared to organize another Tang army against the Arabs when the devastating An Shi Rebellion broke out in 755. When the Tang capital was taken by rebels, all Chinese armies stationed in Central Asia were ordered back to China proper to crush the rebellion.
The Chinese name Daluosi (怛罗斯, Talas) was first seen in the account of Xuanzang. Du Huan located the city near the western drain of the Chui River. The exact location of the battle has not been confirmed but is believed to be near Talas in present day Kyrgyzstan.