jukjusanseong (죽주산성)
Jukjusanseong was originally constructed during the Three Kingdoms Period, most likely by Silla. It was repaired and potentially upgraded during the Goryeo Period with stouter walls. Then again during the Joseon Period with projections which facilitated cannon fire to sweep the base of the fortress’s graceful walls. Jukjusanseong is unique in that it is made up of concentric walls, though each seems to have been built by a succeeding dynasty. The outer wall was built by Silla, the middle wall by Goryeo, and the inner wall by Joseon. All that said, this is the first use of defense in depth I’ve seen in a Korean fortification. More interesting, Jukjusanseong was the site of a 15-day siege by the Mongols in 1234 made famous by a crafty deception by the garrison commander which convinced the invaders to lift the siege and withdraw.