The Battle of Wei River (Chinese: 濰水之戰) was fought in November 204 BC between the Han and a combined force of Qi and Western Chu.
Not only was it the richest and most populous of the northern kingdoms, with Xiang Yu making much use of it to feed his armies; it was also located directly to the north of Chu and would enable Han Xin to invade the Chu heartland to the east of the Central Plain, where Liu Bang and Xiang Yu were caught in a stalemate.
[6] In November the Chu-Qi coalition camped on the south bank of the Wei River, opposite Han Xin’s army to the north.
Upriver, Han Xin secretly constructed a makeshift dam with sandbags to lower the water level.
Long Ju led the vanguard in pursuit, but when only part of his army had made it across the river, Han Xin's soldiers released the dam.
Han Xin subsequently conquered the towns of Ying and Po and defeated and killed the Qi General-in-Chief Tian Xi near Qiansheng.
Liu Bang was angry that Han Xin was requesting a royal title while he himself was struggling against Xiang Yu in the Central Plain, but on the advice of Zhang Liang and Chen Ping, in February 203 he awarded Han Xin the full title of King while the latter was completing the conquest of Qi.
Since 205, he and Liu Bang had worn each other down in a war of attrition in the Central Plain, and Xiang had effectively run out of options to wrest control of northern China from Han Xin.
For these reasons, he chose to remain loyal to Liu Bang and soon coordinated the final campaign against Xiang Yu, which culminated in his victory in the Battle of Gaixia.