Siege of Ansi

The Siege of Ansi was a battle between Goguryeo and Tang forces in the Korean peninsula and a part of First campaign in the Goguryeo–Tang War. The confrontation had lasted for about 3 months from 20 June 645 to 18 September 645.

Background
On 1 April 645, Spearheads of Tang forces led by Li Shiji pretended to march to camp Huaiyuan and suddenly started to invade Goguryeo. They attacked several castles including Shin and Geonan, etc. to muddle defense system of Goguryeo. As the plan had failed, Li Shiji made an array of all of Tang force and they started to attack Gaemo on 15 April. Gaemo was fallen on 25 April. At the same time, the naval forces led by Zhang Liang had landed in Liaodong Peninsula and captured Bisa on 2 May. Meanwhile, Emperor Taizong of Tang joined the forces and they captured Yodong and Baegam one after another. They had decided to attack Ansi and invaded the fortress on 20 June. Against that, Yeon Gaesomun, Generalissimo of Goguryeo, sent about 150,000 forces with Go yeon-su and Go hye-jin to rescue Ansi. However, they had been defeated by Tang and surrendered.

Development
Tang attacked Ansi Fortress with several siege weapons including catapult and battering ram. However Goguryeo repelled the attacks and repaired ramparts each time. Emperor Taizong changed camps many times and announced that he would kill all of men in Ansi when Tang capture the fortress. Tang had built an earthen rampart mobilizing forces of about 500,000 and attacked Ansi with the earthen rampart as a steppingstone. However, the rampart had suddenly fallen and Goguryeo army occupied the rampart. Tang had tried to regain the rampart for 3 days by turning loose on there but Tang failed. In addition, Winter came and food was out. So Tang unavoidably retired.