The Battle of Hulao (虎牢之戰) on 28 May 621 was a decisive victory for the Tang Dynasty prince Li Shimin, through which he was able to subdue two rival warlords, Dou Jiande and Wang Shichong. The battle was fought at the strategically important Hulao Pass, east of Luoyang. Li Shimin led a siege on the city of Luoyang, seat of the self-declared emperor Wang Shichong, who solicited help from Dou Jiande from the east. However, Dou Jiande delayed and when he finally arrived, Li Shimin brought forces to meet the new threat. Li Shimin's army avoided conflict until the troops of Dou Jiande were exhausted and then led a cavalry charge, breaking the opposing army and capturing Dou Jiande. Afterwards, Wang Shichong, seeing no other choice, surrendered Luoyang, and both his and Dou Jiande's states were