Kaesong, the capital of Koryo which was the first unified state of the Korean nation, is famous for many historical relics.
Among them is the relic of drainage facility in Mt Songak, which has been not recorded in such historical documents as History of Koryo , Sinjungdonggukyojisungnam (Revised Handbook of the Korean Geography) and Junggyongji , and not mentioned even in the preceding research data.
As a facility for draining in the Walls of Kaesong which is inscribed in the list of world cultural heritage in 2013, it is located on the northwestern wall near the summit of the hill westernmost of Mt Songak.
The tunnel-type facility, with the cross section of the shape of "ㅍ", a Korean alphabet, is in the centre of the wall facing south; its entrance is 93cm wide and 70cm high and the waterway is 6m long.
The slope of the waterway is peculiar; the two-thirds part from the entrance are inclined at an angle of 10 degrees and the remaining part to the exit is almost horizontal.
The tunnel becomes narrower toward the exit, and the floor is projected by 50cm outside the wall. The water is sprayed outside the wall by the force of the speed at the inclined floor and its horizontal flow.
This structure reflected the intention of the designers to drain water quickly and prevent the damage to the foundations of the wall.
The stone walls near the facility are very similar to the embankment and stone steps of Manwoltae, the site of the royal palace of Koryo. Such an elaborate wall cannot be found in other parts of the Kaesong Walls.
It has been confirmed that the facility was built elaborately soon after Kaesong became the capital of Koryo in the early 10th century.
It is a general practice to build a drainage facility in a lower part of a castle where water interflows. It is a rare example in the world that the artificial drainage facility in Mt Songak, not a natural one, was built near the summit of a hill.
A structure for defending the facility situated about 23 metres to the east is in a good state of preservation. Its construction method is the same as the one of the wall near the drainage facility.
The drainage facility is one of the most typical historical relics in the Democratic People’s Republic of Korea for its long history, peculiar designing and outstanding building methods.
Kim Chol, researcher at section for study of tangible heritage of Korea National Heritage Preservation Agency