Following the Japanese invasion of 1592 and the Manchu invasion in 1627 and again in 1637, awareness of the necessity of national defence was heightened, especially against attacks from the sea. As a result of this awareness, this fortress was built in the 29th year (1703) of the reign of King Sukjong. The inner and the outer walls were mainly built of natural stones, but weak portions were reinforced with artificially worked square stone blocks. The walls are about 17 kilometers in length and from 1.5 meters to 3 meters in height. The area surrounded by the fortress is about 8.2 square kilometers.