In 980, the Liao invasion started with roughly 100,000 Liao soldiers arriving before Yanmen, a pass on the Great Wall in Dai Prefecture and a strategic choke point. After the arrival of Song army commander Pan Mei in Daizhou, Yang and a few hundred cavalrymen took a difficult route on the west, arriving at the north and back of the enemy. As Pan and Yang attacked from both directions, the Liao army suffered a catastrophic defeat: Liao general Li Chonghui (李重誨) was captured; while Emperor Jingzong of Liao's brother-in-law and military governor Xiao Chuoli (蕭啜裏) was killed. Song forces acquired countless horses, saddles, and armor.