the enemy, he decided to go alone to see the Uyghur chieftains. His officers and son Guo Xi () were so dismayed and panicked by his intention that they would not let go of his horse's reins, declaring such an act would be suicide. Guo laughed and convinced his officers to let him go, but his son would not. Angered, Guo whipped his son's hand so that he released the reins, reprimanding him and telling him that this was a life and death situation for the empire; their force was small and if they fought the Tibetans alone, both father and son, and their troops, would die. If he succeeded in his plan the empire would be defended, but if it failed only his own life would be lost. When Guo arrived at the Uyghur's camp, he did not reveal his identity and appeared to be a messenger who had been sent to tell them that Guo Ziyi was coming to see them. The Uyghur chieftains, many of whom had joined the rebel side in the An Lushan Rebellion, were surprised and panicked to hear that Guo was alive, deciding that they had to meet with him. Guo laughed at them and asked them why they would want to face Guo Ziyi again after their defeat at his hands during the An Shi Rebellion. The Uyghur chieftains replied they had been told that he was dead, but if they met with him and saw he was alive, they would retreat. Guo, however, insisted that Guo Ziyi did not seek their retreat but instead wanted them to join him against the Tibetans. The Uyghur chieftains, saying they had been deceived by the Tibetans about Guo's death, agreed to break the alliance with them. They even claimed that shamans had foretold that a great man would lead them to victory and that they now believed this man must be Guo, and agreed to join forces with the Tang. Battle of Xiyuan Guo returned to his camp and ordered a thousand light horsemen to make a quick rush at the Tibetan camp at Xiyuan. When the Tibetans realized the Uyghurs had broken their alliance, they attempted to withdraw, but Guo's horsemen arrived and scattered their forces; at the same time, Guo's Uyghur allies arrived and prevented the Tibetans' retreat. Over 10 000 Tibetans were killed in battle and another 10 000 were taken