This strategically located fort was designed and built by a Japanese general, Kiyomasa Kato, in 1597 during the Hideyoshi Invasion. About 16,000 Japanese soldiers were called out to built it in about forty days out of stones carried from Ulsan p and P`y ngyang fortress. A main fortress (45 meters above the sea) is located in the south of the top (50 meters above the sea) of the mountain, the second fortress (35 meters above the sea) in the lower north of the main fortress, and the third fortress(25 meters above the sea) further down to the west and north of the second. The total fortress's wall is 1300 meters long and 10∼15 meters high. This fortress is double structured by installing a wooden fence (2400 meters) outside of the fortress. The allied army of Korea and Ming China attacked over two times(the first period ; from December 23, 1597 till January 4, 1598 and the second period ; from September 21, till September 25, 1598), but, they failed in taking away it. Afterward, the Japanese escaped to Japan after setting the fort on fire on November 18, 1598 (the 31st year of S njo's reign) following an order to retreat after the commander Toyotomi Hideyoshis's death.