Once called Jeongjoksanseong Fortress, it was also called Samnangseong Fortress since three children of Dangun built it. The time of construction of this fortress is not certain, but it is likely to have been built even before the Goryeo Dynasty. Its palace was built in Samnangseong Fortress in 1259. Judging from the style of the fortress, which followed the style of the period like Samnyeonsanseong Fortress in Boeun and Myeonghwalsanseong Fortress in Gyeongju, however, it was likely built in the Three Kingdoms Period as well. The fortress seems to have been repaired in the Goryeo Dynasty and restored in the 15th year of the reign of King Yeongjo (1739). He built the gate tower called Jonghaeru in the south gate. In the first year of the reign of King Hyeonjong (1660) of Joseon, Joseon wangjo sillok (Annals of the Joseon Dynasty) was moved from the storage in Manisan Mountain to one in Jeongjoksan Mountain. Seonwonbogak Hall, which preserved the royal family pedigree, was also built. Both of them are now gone, and only Jeondeungsa Temple remained. It was famous for mowing down about 160 French soldiers attacking through the east and south gates during the French Invasion of Ganghwa in 1866, the third year of the reign of King Gojong.