The battle of the Wei River (November 204 BC) was a major victory that saw the Han general Han Xin defeat a Chu army that had been sent to defend the kingdom of Qi, allowing the Han to occupy the kingdom of Qi, a strategically important location to the north of the Chu heartland.
Earlier in 204 BC Liu Bang had been forced to escape from the besieged city of Chenggao, and had sought refuge with one of his own armies, commanded by Han Xin. Having secured control of this army, Liu Bang decided to send Han Xin to attack the kingdom of Qi, in the north-east of China.
After sending Han Xin and his army, Liu Bang was convinced by Li Yi Ji, another of his advisors, to attempt to try and convince the king of Qi to change sides peacefully. Li Yi Ji’s mission was a success, but Han Xin either didn’t find out in time or chose to ignore the news, and attacked and defeated the Qi army at Lixia (204 BC). The king of Qi believed he had been betrayed. Li Yi Ji was boiled alive, and Qi then asked for assistance from Xiang Yu king of Chu. Xiang Yu send an army stated to have been 200,000 strong, under the command of Long Ju.
According to the ancient sources Long Ju had a very low opinion of Han Xin, believing him to be a coward (not something supported by his military track record). As a result Long Ju ignored an advisor who suggested that he avoid a battle, denying Han Xin any chance of a victory and hopefully forcing him to retreat.
By November 204 BC the two armies were facing each other across the Wei River, with the Han on the west bank and the Chu on the east bank. Under cover of darkness Han Xin sent part of his army up the river with 10,000 sand bags, which they used to partially dam the river. On the following morning the water levels in the river had dropped so far that Han Xin was able to cross over. He attacked the Chu army, but when Long Ju launched a counterattack Han Xin ordered his men to retreat as if they had been defeated.
Long Ju ordered his men to cross the river in pursuit. At a key moment Han Xin gave the signal and the sandbags were removed. The water levels rose, isolating Long Ju and a small part of his army on the west bank. Han Xin turned back and crushed Long Ju and his isolated men. Long Ju was killed in the battle, while Tian Guang, king of Qi, was captured and killed soon after the battle.
Tian Guang was succeeded by Tian Heng, but he was defeated in battle at Ying (204 BC). Tian Xi, the commander-in-chief of Qi, was defeated and killed at Qiansheng. Finally Tian Ji was attacked and killed, ending resistance in Qi.
In the aftermath of his triumph Han Xin asked to be made King of Qi, claiming that the area would revolt unless he was given this authority. Somewhat reluctantly Liu Bang acknowledged Han Xin as king of Qi. The events of 203-202 BC suggest that Han Xin now saw himself as at least semi-independent, for when Liu Bang summoned him to take part in the final campaign against Chu the new king didn’t turn up until he was offered a major extension to his kingdom.