窦建德
The Battle of Hulao () or Battle of Sishui (汜水之戰, Wade–Giles: Ssŭ Shui), on 28 May 621 was the main and final battle of the Luoyang–Hulao campaign between the rival Tang, Zheng, and Xia regimes during the transition from Sui to Tang. It was a decisive victory for the Tang prince Li Shimin, through which he was able to subdue two rival warlords, Dou Jiande who headed the Xia regime in Hebei, and Wang Shichong, the self-declared emperor of the Zheng dynasty. The battle was fought at the strategically important Hulao Pass, east of Luoyang.