Busosanseong Fortress is a mud fortress located on top of Busosan Mountain (altitude 106 meters) in the northern part of Buyeo. The fortress is estimated by some to have been built around AD 538 to protect Sabi (now Buyeo), which was once the capital of the Baekje kingdom (18 BC-AD 66). Other historians, however, believe that the fortress was already in place by AD 500 and modified in 605 into the structure we see today. In either case, some parts of the fortress were reconstructed during the Unified Silla period (676-935) and modified again in the Goryeo (918-1392) and Joseon (1392-1910) eras.

Busosan Mountain is home to historic landmarks from the Baekje kingdom, including the archaeological site in Gwanbuk-ri, located just in front of Buseosanseong Fortress. Within the fortress, some of the most famous sites include Baekhwajeong Pavilion, Sajaru Pavilion, Banwollu Pavilion, Yeongillu Pavilion, Samchungsa Shrine (dedicated to three loyal subjects of the Baekje kingdom), Gungnyeosa Shrine, Goransa Temple, Gunchangji (military warehouse site), and Suhyeoljugeoji (site of pit houses for the Baekje soldiers). The mountain is also home to Nakhwaam Rock where, according to legend, 3,000 women of the Baekje kingdom threw themselves into the river below after the collapse of the empire.