Battle of Hulao
621 CE.
Shown on the map at 34.844°, 113.206°.
The Battle of Hulao, (Chinese: 虎牢之戰) or Battle of Sishui (汜水之戰, Wade–Giles: Ssŭ Shui), was a decisive Tang victory over the rival Zheng and Hebei-based Xia polities during the transition from Sui to Tang. The battle took place during the Luoyang–Hulao campaign on 28 May 621 when a Xia army – led by Dou Jiande, ruler of Xia – was defeated attacking a smaller Tang army – led by Prince Li Shimin – entrenched at the strategic Hulao Pass. Li launched the Luoyang–Hulao campaign in August 620, attacking eastwards and quickly besieging Wang Shichong, ruler of Zheng, in Luoyang. Zheng attempts to break the siege failed, and they appealed to Xia for help. In April 621, Dou led a Xia army of 100,000–120,000 troops westward to break the siege. Instead of retreating back to the Tang heartland in Shanxi, Li maintained the siege and took a small part of the Tang army further east to the Hulao Pass to block the Xia. A stalemate ensued for a few weeks; the Tang refused to fight outside of their positions, and the Xia refused to outflank Li or redirect their offensive to Shanxi. Li broke the stalemate at the end of May by feinting the departure of a large part of the Tang cavalry.
Text from the Wikipedia article Battle of Hulao, licensed CC BY-SA 4.0.