778 Dong-i-ri, Misan-myeon, Yeoncheon, Gyeonggi-doShow Map
Dangposeong is the Goguryeo era castle formed between Danggae Creek flowing into Dangpo Naru and Imjin River main stream and located on the land on the flat triangular-shaped cliff. As a riverine flatland fortress found only in the north shore of Imjin River·Hantan River of Yeoncheon County, it is called one of Goguryeo’s three fortresses with Horogoruseong, Eundaeri fortress and both location conditions and plane form are similar.
Vertical basalt columnar joint cliffs developed along Imjin River and Hantan River provide a naturally blessed strategic hub that can easily block enemies without creating separate castle walls. But, small rivers flowing into Imjin River supplemented the vulnerable defense point by building castle walls in a place where basalt cliffs are supposed to be drilled.
As above, Dangposeong also corresponds to a castle built to reinforce the fallen cliff because of the creek. Columnar joints under Dangposeong develop radially and vertically and many river cavaes were created by the erosion of the river. And it is a region where lava moved farthest and the thickness of the basalt layer seems to be relatively thinner compared to the top.
Dangposeong has been never mentioned in various geological documents published during the Joseon Dynasty and there is only a record in Gieonui 『Gieonbyeoljip』 Vol. 15 「Musuljuhanggi」 of Mi Su Heomok a hiistorical figure in Yeoncheon, saying ‘…There was an old jinru on the hill river wall in front of Majeon and now there is a shrine to various gods on it and a dock in front of it is called Danggae and large water flows and leads to the dock road.’ Making the most use of the terrain, the castle walls of Dangposeong were built by stacking stones only in the east connected to the plains not forming a vertical cliff. For the eastern castle wall, length is 50 m, residual height is about 6m and the length from the eastern wall to the west end of the castle reaches about 200m.
Basalt often available in the surrounding was used to build the castle and this is one of the great features of Goguryeo castles. Since Majeonhyeon corresponding to the crossroad to Gaegeong behind Dangposeong, Dangposeong can be said to be essential for defending the enemy moving northward in the shortest distance from Yangju Basin. On the other hand, it seems to have been used consistently even during the occupation period of Silla because a foothold should be ensured in the north shore of the river while moving northward.