A fortress in the Geumgang River area, Gongsanseong is one of the earliest walls made to protect Gongju, the capital of the Baekje Dynasty. It was originally earthen walls but rebuilt with stones in the Joseon Dynasty. The exact date of its construction is unknown. What is known is that it was called Ungjinseong Fortress during the Baekje Dynasty, Gongjusanseong Fortress or Gongsanseong Fortress during the Goryeo Dynasty, and finally Ssangsusanseong Fortress since the Joseon Dynasty. There were four gates in the fortress, but only two of them remained before 1993: Jinnamnu Pavilion in the south and Gongbungnu Pavilion in the north. In 1993, the other two gates, Yeongdongnu Pavilion in the east and Geumseoru Pavilion in the west were restored. Other remains include -- in addition to a number of military facilities -- Ssangsujeong Pavilion, Yeongeunsa Temple, Yeonji Pond, Imnyugak Pavilion site, and Manharu Pavilion site. Many pieces of Baekje tiles including the lotus-patterned one, earthenware, and other relics from the Goryeo and Joseon Dynasty were also found. This is the place where King Uija stayed for a short time after the fall of the Baekje Dynasty and where the Baekje Restoration Movement got its power. It is also where the rebellion by Kim Heon-chang (822) took place in the Unified Silla Dynasty and where King Injo of the Joseon Dynasty took refuge following the revolt by Yi Gwal (1623). It had been the capital of Baekje Dynasty until King Seong moved it to Buyeo in 538; since then, it has continued to be treated as an administrative hub of the region.

公山城是在百济首都为公州的时期守护公州的山城。山城环绕锦江边的山中溪谷而建，原为土城，后来在朝鲜时代翻修为石城。筑城年代不详，百济时期被称为熊津城，高丽时代被称为公州山城·公山城，朝鲜仁祖以后称为双树山城。四方皆有门的遗址，现留存有南门镇南楼与北门拱北楼，东门与西门只剩下门的遗址，1993年复原了东门遗址迎东楼与西门遗址锦西楼。公山城在百济圣王16年(538)迁都扶余之前曾是百济的都城，后来至朝鲜时代为止一直是地方行政的中心地，是具有悠久历史价值的遗址。

公山城は百済の首都が公州であった時、公州を守った百済の山城である。錦江岸近くの野山の谷を囲んだ山城で、元々は土で築いた土城であったが、朝鮮時代に石城に建て直した。築かれた年代は明らかになっておらず、百済の時には熊津城として、高麗時代には公州山城・公山城として、朝鮮時代仁祖以降には双樹山城と呼ばれた。四方に門の跡が確認されているが、南門である鎮南楼と北門である拱北楼が残されており、1993年には東門の跡の迎東楼を、西門の跡の錦西楼を復元した。百済聖王16年(538)に扶余に都を移す時までの百済の都城で、その後にも朝鮮時代まで地方行政の中心地であった所で、歴史的な価値が大きい重要な遺跡である。