Following the fall of the Qin dynasty in 206 BC, Xiang Yu, who had declared himself "Hegemon-King of Western Chu", appointed Long Ju as a general in his army.
After Xiang Yu defeated Liu Bang at the Battle of Pengcheng in 205 BC, he put Long Ju in command of his elite cavalry forces composed of hired Xiongnu warriors.
In 204 BC, Liu Bang sent his general Han Xin to lead a separate force to attack Qi.
The combined strength of the Chu and Qi forces, under Long Ju's command, was around 200,000 when they engaged Han Xin and his troops at the Battle of Wei River in present-day Weifang, Shandong.
During the battle, Han Xin feigned defeat to put Long Ju off guard and lure him into a trap.