Danyang Jeokseong Fortress is a fortress made of stone from Seongjaesan Mountain in Danyang. About 900 square meters of the surrounding area was mostly destroyed, but in the northeast section, the inner wall of the part that was heaped across the wall still remains. The castle was built surrounding the mountain's southern slope and around the summit. It was designated as Historical Site No. 265 in August 1979. Also, the circumference of the fortress is 923 meters, but most of the fortress walls have collapsed. A 3-meter section of wall remains at the end of the northeast part. Three gates were found in the southwest, east, and southeast areas. Inside of the fortress is the Jeokseongbi stone stele. Jeokseong Fortress is also called Jeoksanseong, as the place was an outpost for the Silla army's invasion of the north, where they stole Goguryeo army’s compound. * Historical symbol of Jeokseongsanseong Fortress Jeokseongbi Stone Stele was found in 1978 inside of the fortress. This artifact relates the power struggle between the Silla and Goguryeo. Besides the stone stele, the fortress also houses relics from the Three Kingdoms Period, such as earthenware and tiles from the Goryeo period. Also, the method employed to construct the structure resulted in its sturdiness, and thus the fortress has important value for studying fortification.