The Battle of Wei River was fought in 204 BC between the Han and a combined force of and Western Chu. The famous general Han Xin led the Han force, while the Qi were led by Prince Tian Guang , and the Chu were led by Long Qie . It was one of the most important battles of the Chu-Han Contention.
In 205 BC, Han Xin had captured most of the modern Hebei and Shanxi provinces, the principalities of , and , and was starting to march on the principality of Qi. At this time, Prince Tian Guang, persuaded by noted diplomat Li Yiji , had decided to acknowledge the leadership of Han and its king Liu Bang. However, Liu Bang did not officially notify Han Xin of this fact. Ignorant of Prince Tian Guang's intentions Han Xin decided to launch a surprise attack against Qi, under the counsel of Kuai Che . Tian Guang's forces were completely surprised. Tian Guang fled and sought assistance from King Xiang Yu of Western Chu, pledging fealty. Xiang Yu sent a strong expeditionary force, including some elite cavalry, under Long Qie to relieve Qi.
Han Xin knew that Long, noted for his personal bravery and fighting prowess, was too arrogant. The night before the battle, he set a trap for Long by building a makeshift dam with sandbags to lower the water level in the Wei river. Long was counseled to fight a slow battle of attrition since he had forces to spare . Long declined, believing he had overwhelming forces. Long also believed Han Xin was a coward, as a result of an incident when Han Xin served in the Chu forces. In this well-known incident, Han Xin crawled between the legs of some hooligan to avoid conflict when he was outnumbered.
The next morning, Han Xin marched across the lowered river and attacked Long's forces. Then made a strategic retreat, tricking Long into charging his army across the river. When about one quarter of the Chu army had crossed, Han signalled for his men to open the dam. This succeeded both in drowning many of the Chu soldiers, and isolating Long Qie with only a fraction of his force. Cut off by the river, Long Qie had nowhere to go and was cut down in battle. The rest of the Chu army disintegrated when Han Xin continued to press his attack. Prince Tian Guang fled and was eventually caught and killed.
This battle was strategically significant because it cost Xiang Yu between half and a third of his forces, including many veterans, depleted Chu of important reserves and prevented any future possibility of Xiang Yu fighting successfully on two fronts. Eventually, Xiang Yu was deprived of elbow room and lost the war.
It was worth noting that Xiang Yu, for some reason, did not lead the Chu army into battle himself, when fighting against the by then well-known Han Xin.