Battle of Hulao: Li Shimin, the son of the Chinese emperor Gaozu, defeats the numerically superior forces of Dou Jiande near the Hulao Pass (Henan). This victory decides the outcome of the civil war that followed the Sui dynasty's collapse in favour of the Tang dynasty.

The Battle of Hulao, or Battle of Sishui, 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.