Korean History › Three Kingdoms › Goguryeo
Siege of Ansi Fortress
645· Battle· Wars & invasions
Mostly agreedGood evidence; some details, dates or numbers uncertain.
In 645 a Goguryeo fortress held out for about three months against Tang Emperor Taizong, forcing his invasion to retreat.
See it on the Korean History map →What happened
Tang Emperor Taizong invaded Goguryeo in person in 645, citing the strongman Yeon Gaesomun's 642 coup. He took Liaodong and other fortresses and routed a Goguryeo relief army reported at 150,000. Then his army stalled at Ansi Fortress (안시성), in today's Liaoning province, China. Tang troops built a huge earthen ramp to top the walls; when part collapsed, the defenders seized it. With winter coming and supplies low, Taizong withdrew.
Why it matters
It ended Tang's first invasion of Goguryeo and convinced Tang it needed a Korean ally: Silla.
How we know
The Old and New Tang histories, the Zizhi tongjian chronicle and the Samguk sagi describe the siege in broadly matching terms.
Still debated
The commander's name, Yang Man-chun, appears only in much later sources. The story that Taizong lost an eye to an arrow is legend. Ansi's exact site is debated.
Connections (2)
▸Siege of Ansi Fortress turned back Tang's attack on GoguryeoMostly agreed
The connection
Taizong took several Liaodong fortresses in 645, but Ansi's long resistance pinned his army down into autumn. Short of supplies, he retreated with heavy losses. Goguryeo survived, and smaller Tang raids in 647–648 also failed, pushing Tang to seek an ally in Silla.
When and how
Summer to autumn 645, at Ansi in the Liaodong region (today's Liaoning, China); Taizong led in person against Yeon Gaesomun's Goguryeo.
How sure are we?
Chinese histories admit Taizong's withdrawal; the Samguk sagi agrees and adds Korean details.
Debates and open questions
Tang losses are uncertain: Chinese sources play them down, while Korean tradition enlarges them.
▸Battle of Salsu River under Eulji Mundeok foreshadowed Tang's own failure at Siege of Ansi FortressMostly agreed
The connection
Sui's disaster at Salsu showed that huge Chinese armies struggled with long supply lines, short campaign seasons and Goguryeo's fortress defense. Tang, which replaced Sui in 618, met the same problems at Ansi in 645: stalled before walls, it had to retreat before winter.
When and how
Thirty-three years apart: Salsu in 612 under Sui's Emperor Yang, Ansi in 645 under Tang's Emperor Taizong, who had watched Sui collapse.
How sure are we?
This is an interpretive link. Both campaigns are well recorded, and Chinese accounts of each describe the same supply and seasonal problems.
Debates and open questions
Whether Goguryeo's defensive skill or China's logistical limits mattered more is debated.