The Battle of Yijing was a military conflict which took place in northern China from 198 to 199 in the late Eastern Han dynasty.
The two warlords had been fighting for dominion over northern China for some time, but eventually Yuan Shao gained the upper hand.
There were ten moats around the fortress and the towers had iron doors with huge grain supplies for Gongsun Zan to use to live out the civil wars in northern China.
Gongsun Zan then took Guan Jing's suggestion to withstand the siege until the time when Yuan Shao would be forced to retreat.
Yuan Shao's troops followed up their success by digging tunnels under Yijing and then supporting them with beams, which they later torched.