The respected Comrade
"A valuable legacy created by our ancestors through their struggle and creative activities, historical sites and relics are an asset of the nation that should be handed down from one generation to the next."
Among the excellent cultural assets created by Korean ancestors are the ponds built in the castle on Mt. Taesong in the period of Koguryo.
Those in Taesong District, Pyongyang, were very important facilities used to defend the castle.
In the medieval ages, warfare was under way in the castle with the gates closed, so it was necessary to have much water inside as well as a large number of soldiers, weapons and military supplies for prolonged fights.
When they fought in defense, there were not only soldiers defending the castle but also the people who had come to escape from the war and a large number of military horses and livestock and consequently, drinking water became inevitable.
According to the article from "Samgukshagi"(The Chronicles of the Three States) related to the battle in Liaodong Castle during the war of Koguryo-Tang in 645, there were totally more than 60, 000 soldiers and inhabitants in the castle.
Assuming that a person drinks about one litre of water a day, it is believed that about 60,000 litres (about 60 tons) of fresh water was consumed by soldiers and ordinary people a day.
Water was used not only for drinking but also as important means to defend the castle in the middle ages. In other words, soldiers prevented the enemy's attacks by pouring the boiling water over the enemy soldiers who climbed the walls.
It was also needed for fire-fighting when buildings in the castle, including general terraces and pavilions, were on fire.
Therefore, water was regarded as one of the important factors to assess the ability to defend the castle at that time.
Then, the castles of several countries in Asia and Europe were mainly built by surrounding the city located in the flatland.
In those cities, rivers nearby were used as the source, so there was no big problem with water, but in the castles of Koguryo which were built on the mountains, it became a pressing problem.
People in Koguryo built the castle on Mt. Taesong and established regular water supply system, in keeping with the characteristics of the mountainous areas with the poor source of water, thus ensuring a large amount of clean water.
Water supply system in the castle consisted of the source of water, water-drawing structures and pipelines to supply water.
They discovered underground water and made effective use of water flowing through hills and valleys.
The seven wells and other ponds found inside the castle, such as "Carp Pond", "Deer Pond", "Kuryong Pond" and "Jangsu Pond", which are never dried in all seasons, show that the people of Koguryo actively used the underground water that was abundant in quantity and high in quality.
And the mountain has several valleys, so there was a stream of water flowing through them, which could also be used as the source of water.
Water-drawing channels were built to provide the required amount of water from the source of water, whose number amounted to 170.
Most ponds were squared, but some of them were round or triangulate.
They were made up of stones properly faced like those of a citadel in a neat and strong way and bottoms were covered with gravel on top of the mud so that fresh water was always stagnant.
They were also piled up repeatedly to consolidate the embankment, and ditches were formed out of it to prevent dirt from flowing straight into the pond or filling up the pond even when the water was suddenly overflown in the rainy season, so that people could always drink fresh water.
The source of water and water-drawn channels in the castle on Mt. Taesong were all linked to the waterways.
170 ponds there were located in several places to form a group and connected to each other by channels, taking water from the source in turn to fill the pond, and then making it flow into next one.
Channels were all built of stones underground, being filled with large stones and gravel to allow the water to flow out and to be filtered out.
Like this, 170 ponds were linked by underground channels to make use of all the source of underground water and to form a regular water supply system.
The water supply system was very excellent at that time.
It can be found in its design where almost all the ponds were to serve both as water supply and purification functions.
First, channels were built of stones with boulders and pebbles inside to filter the water first. In addition, pebbles were stacked at the entrance of the pond so that the water flowing into the pond was filtered once again.
And most of the ponds in the castle had embankments to let water flow along the ditch at the edge of the pond and permeate through the pond into the central part of the pond and into the surrounding wells for final filtration. The method of water filtration using stones and sand is also used in many parts of the world now.
Second, the ponds were designed and constructed to maximize the hygienic stability of drinking water, the abundance of supplies, the ease of use and management of water supply facilities, safety and durability in accordance with their mission and usage.
The structure of 170 ponds was designed to serve both as water supply and filtration and was located near the barracks or along the castle for ease of use.
Also, double and triple ditches were dug around the pond to facilitate the management and operation of the pond so that dirty water could turn around the pond ditch and sink into spillway ditch in the rainy season. This made it impossible to fill up the pond and easy to dig out the soil that found its way there because the soil that had been washed away would be piled up in the ditch. This was a unique method invented by Koguryo people in building ponds, as it was derived from a careful consideration of the topographical condition in which they were situated in the hollow places, not the plain, and the weather conditions of the country that heavily rained every year.
And the ponds were built as if constructing walls with standardized stones like those of a castle, so that they remain almost as they were today, a thousand and hundreds of years later.
Third, water supply system was designed to let water flow in a natural way.
In conformity with the features of the mountainous area where the source of water are scarce, Koguryo people found out the stream of spring and built water-drawing structures and formed a gravity-driven water-supply system by transferring the overflowing water through the underground channels to the ponds below.
This was the result of their painstaking efforts to improve the ability to defend the castle by securing the source of water as much as possible and the product of the systematically accumulated environmental control technology, which made a great contribution to raising the defense capability to the maximum as well as creating the scenic beauty.
Koguryo people who were possessed of such a high sense of patriotism, outstanding wisdom and talents, built the castles, fortress of defense, strongly and secured the source of water sufficiently as well as weapons and military provisions. Therefore, no matter how ferocious aggressors might attack and no matter how long they had to fight against them, they defended their fortress without flinching from any siege and finally won victory.
The ponds are still admired by many people for their excellent qualities, showing the wisdom and talents of Korean nation.
