Haengju Sanseong is a mountain fortification built with earthen walls along the ridge of 70~100 meters in elevation with the summit of Mt. Deokyang at Haengjunae-dong, Deokyang-gu, Goyang, which is 124.8 meters above sea level being the center. Whole length of the wall is about 1Km. In the south, the fortification borders Han River. In the southwest, Changreung-cheon river flows around the fortification and into Han River making a natural moat. Very steep slopes in the southwest and south form a natural protective wall. The fortification consists of the inner castle surrounding the peak of a hill close to the river and the outer castle surrounding a small ravine opening to the north. It is unknown exactly when the fortification was built. But the construction method utilizing steep riverside cliffs and shape of the site encompassing wide plains in the northeast resemble the fortifications constructed in early days of the 3 Kingdom Era. Especially, this fortification is well known for the victory won by General Kweon Yul in 1593 during the reign of King Seonjo against invading Japanese forces. The victory is one of the 3 major victories won by the country during the Japanese Invasion.

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