Mongchontoseong Fortress is an earthen fortification from the Baekje dynasty (18 BC - AD 660). It was built sometime between the 3rd and 4th centuries, using the natural protection offered by a tributary to the Hangang River on one side and wooden barricades for added defense on the other side. The fortress has been designated as Historic Site No. 297, and is currently located inside Seoul Olympic Park.

Mongcheontoseong Fortress features an overlapping structure of the outer and inner fortifications that were built along the hill lands descending down from Namhansanseong Fortress. On display inside the fortress are artifacts excavated from the site that date back to the Baekje dynasty. The exhibited items include various earthenware and living tools. The site also displays dugout hut and storage pit sites in the state they were at the time of excavation.