Mongch'ont'osŏng (Korean: 몽촌토성; Hanja: 夢村土城) is an ancient earthen rampart dating from the Baekje period.

The fortification walls are estimated to have been about 2.7 km (1.7 mi) in length and approximately 6 to 7 m (20 to 23 ft) high.

The fortifications of Mongch'ont'osŏng had a palisade atop the wall and a moat surrounding its base.

During the 1988 Summer Olympics, the running section of the modern pentathlon was held there.

[citation needed] A number of important excavations of the site were conducted prior to the construction of the nearby Olympic Park.