The Battle of Huoyi (霍邑之戰; Wade–Giles: Huo-i) was fought in China on 8 September 617, between the forces of the rebel Duke of Tang, Li Yuan, and the army of the ruling Sui dynasty. Li Yuan, with an army of around 25,000, was advancing south along the Fen River towards the imperial capital, Daxingcheng. His advance was stalled for two weeks due to heavy rainfall and he was met at the town of Huoyi by an elite Sui army of 20,000 (or 30,000) men. Li Yuan's cavalry, under the command of his two eldest sons, lured the Sui out of the protection of the city walls, but in the first clash between the two main armies, Li Yuan's forces were initially driven back. At that point, possibly due to a stratagem on Li Yuan's behalf, the arrival of the rest of the rebel army, or to the flanking manoeuvres of