The battle of the Si River (203 BC) was a major victory won by Liu Bang over a Chu army that had been defending the city of Chenggao.
Cao Jiu and Sima Xin, King of Sai, the commanders of the Chu army at Chenggao had been given strict orders not to fight a battle until Xiang Yu returned from supressing a revolt in the east. When Liu Bang arrived outside the city Cao Jiu refused to come out and fight. Liu Bang’s response was to order his men to taunt the defenders of the city. After five days of this treatment Cao Jiu lost his temper and decided to come out and fight.
Liu Bang’s army was positions on the opposite bank of the Si River (Wade-Giles Szu), a southward flowing tributary of the Huai River. In 1194 the Yellow River shifted its course to the south, swallowing up the Si River. When the Yellow River eventually returned to its northern course the bed of the Si River was blocked.
Liu Bang waited until half of the Chu army had crossed the river, and then launched his attack. Caught in the middle of the water, the Chu army suffered a heavy defeat. Liu Bang captured a great deal of treasure, including gold and jewels (perhaps suggesting that Cao Jiu was actually planning a retreat to the east). Cai Jiu and Sima Xin both committed suicide during the disaster.
The defeat at the Si River forced Xiang Yu to return west to try and restore the situation. He forced Liu Bang to abandon the siege of Zhonglimo, but the Han then took up strong defensive positions and a stalemate developed. Xiang Yu’s troops were increasingly short of supplies, and he now accepted peace terms that had been offered during 204 BC. In the treaty of the Hong Canal Xiang Yu was to keep eastern China while Liu Bang got the west. The Hong Canal was to mark the boundary between the two kingdoms.
This would be a short-lived peace. In 202 BC Liu Bang broke the agreement, invaded Chu, and defeated Xiang Yu at Gaixia. Xiang Yu escaped from this battle, but was soon trapped and committed suicide, effectively ending the Chu-Han Contention.