the emperor largely ignored this. Tibetan invasion of 763 In 763, a force of 100 000 Tibetans invaded the Tang. Daizong fled Chang'an on 16 November when it became clear the city would be captured. The Tibetans crowned Li Chenghong as emperor of Tang in Chang'an, but retreated a month later fearing a Tang army had arrived. In reality Guo ordered cavalry scouts to go forward and light fires, in places where the enemies could see, and then retreat. Guo also sent secret messages to Chang'an, ordering citizens to strike gongs and create fire. The Tibetans, confused by these actions, panicked, scattering when the rumor spread that Guo Ziyi moved against them with a large force. With the Tibetans retreating from their positions, the invasion was concluded without loss to either side. Many Chinese military historians consider this victory to be the best example of Sun Tzu's idea of the cleanest kind of battle, "a war with no loss on either side but simply played out with the desired effect for the victor." There are discrepancies in the number of cavalry Guo dispatched; Chinese sources state that Guo had sent out only 13 scouts, but a Tibetan text indicates there had been 200. Nevertheless, the Tibetan army retreated, and when Guo Ziyi arrived at Chang'an with his "large" force, Daizong appeared to him and stated, "By employing the Elder not sooner: so many deaths reached, woe is this!" 「用卿不早，故及於此。」 Tibetan invasion of 764 The Tibetan Empire invaded again in 764 with a force of 70,000 but was repulsed in Jiannan by the jiedushi Yan Wu. Tibetan threat of 765 and the Uyghur alliance The Tibetans attacked again in 765, when the Tiele jiedushi Pugu Huai'en sent false messages to Trisong Detsen, the emperor of Tibet, stating that Guo Ziyi had died. The Tibetan emperor was eager to avenge his earlier defeats, and dispatched a large force to attack Tang China again. Various Uyghur chieftains, also believing that Guo was dead, joined force with the Tibetans. The Tibetan force was recorded as more than 30,000 (including a few thousand Uyghurs), almost the entire Tibetan military at the time. However Pugu died on 27 September, and his army defected to the Tang. When news of the Tibetan attack reached Emperor Daizong, he dispatched Guo Ziyi to defend the Tang with only few thousand men. When Guo was within a day's march from