Samguk Sagi, a history of the Three Kingdoms period of Korea.
The Samguk Sagi was written on the basis of the Gu Samguksa (舊三國史, Old history of the Three Kingdoms), and other earlier historical records such as the Hwarang Segi (花郞世記, Annals of Hwarang) , most of which are no longer extant.
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Furthermore, through the Samguk Sagi, Kim Busik praised a castellan of Goguryeo who defeated The Emperor Taizong of Tang at the Siege of Ansi Fortress and judged the Goguryeo castellan a hero.
The first mention of this fortress in historical records comes from the Samguk Sagis statement that King Chaekgye of Baekje ordered it to be fortified against an expected Goguryeo invasion.