After the Yan army captured most of Northern China by 756, remaining Tang forces rallied around the newly-enthroned Emperor Suzong in Lingwu, and by 757, with Yan forces having become severely depleted following the Siege of Suiyang and a series of costly campaigns in modern day Shanxi, the Tang army was prepared to counterattack. After a setback in May 757 in which Tang forces were defeated by a Yan cavalry attack at the Battle of Qingqu [zh], in October 757, a large Tang field army composed of forces from the Shuofang and Anxi military districts as well as Uyghur and Arab auxiliaries was amassed in Fengxiang under the nominal command of Li Chu, with Guo Ziyi serving as the actual field commander.[1][2] The Tang army attacked Yan forces around Chang'an on 29 October, 757.
On 13 November, the Tang and Yan armies clashed on the plains to the Northwest of Chang'an by the Xiangji Temple. The Tang vanguard were led by Li Siye, who oversaw the infantry from the Anxi and Beiting garrisons. Guo Ziyi held command in the central army, with the Shuofang army as his main force, supported by troops from Khotan and others, while Wang Sili [zh] commanded the troops of the Guannei headquarters army as the rear support. Additionally Pugu Huai'en, a Tang general of Tiele descent, led 4,000 Uyghur cavalry concealed on the eastern flank of the main force serving as an ambush force. The Yan army was led by generals An Shouzhong [zh] and Li Guiren [zh], commanding 100,000 troops including Yeluohe cavalry (mostly of Khitan, Kumo Xi, and Turkic origin) and the Kelan and Jinglue armies.
At noon, the Tang army seized the high ground of the hills northwest of Xiangji Temple, stretching their formation over thirty li. The Yan forces, placing themselves against the city of Chang'an facing south, arrayed their 100,000 troops over ten li, with cavalry placed on the eastern side of their formation. At noon, the rebel general Li Guiren led more than ten thousand cavalry in a charge against the vanguard infantry led by Li Siye. At the beginning of the battle, the Tang forces were at a disadvantage until Li Siye, bare-chested and wielding a glaive, charged into the Yan formation and killed dozens of rebel soldiers, stabilizing his own formation. He then led 2,000 glaive armed troops in repeated charges against the enemy cavalry. The battle became deadlocked, and several thousand of Yan's armored cavalry, commanded by An Shouzhong, attempted a flank attack, intending to encircle the Tang forces by repeating tactics used earlier during the Battle of Qingqu. However, this move was anticipated by Guo Ziyi, who had 4,000 Uyghur heavy cavalry hidden on the side and rear, who then charged down from the high ground and significantly damaged the cohesion of the Yan army.
The Yan army continued to hold their formation until late in the afternoon, until finally collapsing due to high casualties, with 60,000 beheaded[2] and Yan general Zhang Tongru [zh] abandoning Chang'an and fleeing east.[1]
The Tang army lost 70,000 men during the battle, with the Anxi and Beiting armies being nearly decimated. Yan casualties were also heavy at 80,000, and the bulk of their forces stationed around Chang'an were destroyed. An Shouzhong gathered his remaining forces and retreated back to Chang'an, then abandoned the city and continued retreating east during the night. Tang forces under Li Chu and Guo Ziyi recaptured Chang'an on 14 November, the day after the battle.[2]
