.Fortresses of the Three Kingdoms Period
.As warfare intensified during the Three Kingdoms period (1st century B.C.-A.D. 7th century), this led to a proliferation of fortress construction. According to Samguksagi (History of the Three Kingdoms), Goguryeo built numerous fortresses, beginning with King Dongmyeong’s fortress and palace in 33 B.C. The wall murals of the tombs found in former Goguryeo territory depict fortresses, confirming that Goguryeo long possessed highly advanced fortress construction techniques.
.Goguryeo primarily built mountain fortresses that capitalized on the natural topography to produce highly effective strongholds. Goguryeo developed fortress-building techniques earlier than Baekje and Silla. Not only did it install various structures, such as redands, ramparts, and ongseong (a semicircular wall designed to guard the main fortress), but it also applied advanced civil engineering techniques in building the fortress walls. As such, thanks to their strategic locations and construction innovations, Goguryeo mountain fortresses occupy a special place in the history of Korean construction.
.The Baekje Kingdom (18 B.C.-A.D. 660) also built many mountain fortresses, including Masuseong Fortress and Byeongsanchaek Palisades in 11 B.C. during King Onjo’s reign. Initially, Baekje focused on the construction of fortresses along the Hangang River, then after relocation of its capital to Ungjin and later Sabi, it built additional fortresses in these areas.
.Various references document the Silla Kingdom (57 B.C.-A.D. 935) construction of fortresses, such as Geumseong Fortress built in 37 B.C. nearby the capital. Wolseong Fortress in Gyeongju and the wooden palisades of Dalseong Park in Daegu are the remains of early Silla fortresses. Wolseong Fortress consisted of a semicircular fortress that housed a Silla palace and auxiliary buildings.
.As conflict between the three kingdoms of Goguryeo, Baekje and Silla further intensified, they began to develop military systems far larger and more organized than existing nations or groups, which fundamentally altered the face of warfare on the Korean peninsula. Not only did war become routine, but as large-scale battles increased, which required the mobilization of ever-greater numbers of troops, the defensive facilities needed to be reinforced and expanded in various ways. More fortresses were built at this time than in any other period of Korean history. Many mountain fortresses were constructed, particularly at strategic locations of each area and along frontier regions on the borders of the individual kingdoms.
.Foundation of National Defense System
.With the start of the Goryeo Dynasty (918-1392), the nation’s defense system was restructured to protect the capital of Gaeseong. Over a period of about 12 years, Goryeo built the Great Wall of a Thousand Ri, which extended from the mouth of the Amnokgang River, through the mountainous regions along the upper reaches of Cheongcheongang River and Daedonggang River to the east, and on to Yeongheung. Goryeo also built numerous fortresses throughout the nation. It allocated all available resources to ensure the proper maintenance and operation of mountain fortresses to defend against aggression by any outsiders. This included the dispatch of mountain fortress officials to oversee the fortresses.
.With the founding of the Joseon Dynasty (1392-1910), it established Hanyang (modern-day Seoul) as its capital. With Ming China having consolidated its position in the north, Joseon revamped its defensive system to counter this threat. City walls were built to protect Hanyang, while fortress facilities around the nation were renovated. King Taejong, the third ruler of Joseon, faced threats not only from Japanese marauders but also escalating tension in Northeast Asia as Ming China campaigned against the Tartars and pressured the Jurchen. Thus, he not only built mountain fortresses at strategic locations in the north, but also developed large-scale mountain fortresses in the Gyeongsang-do provinces in the southeast and Jeolla-do provinces in the southwest.
.From the time of King Sejong (r. 1418-1450), however, extensive town walls were established such that the defensive system centered on mountain fortresses began to decline, which led to their neglect and deterioration.
.In fact, by the mid-16th century, only about 41 mountain fortresses remained operational nationwide. Although the city walls were built on flatlands, they differed from conventional flatland fortresses, like those seen in China or Japan. In particular, they reflected efforts to adapt the advantages of mountain fortresses, in terms of observing enemy movement, defending against invaders, and requiring limited resources, to the design of flatland fortress.
.In the late Joseon period, the nation suffered through such devastating onslaughts as the Japanese Invasions of 1592-1598 and the Manchu Invasions of 1636-1637, that it became necessary to critically reassess the existing defensive system. There was also active discussion of the city- wall defense system, as well as the maintenance of fortresses in the border regions. In this regard, Namhansanseong, Bukhansanseong, and Tangchundae-seong mountain fortresses, as well as Suwon’s Hwaseong, were either reconstructed or reinforced. Bukhansanseong was built as an emergency safe haven when the government, including the king, might not have enough time to retreat to Ganghwado Island or areas south of the Hangang River in the event of a crisis. As turmoil heightened in the 19th century amid the aggression of Western powers, mountain fortresses in coastal areas, including Ganghwado Island, were renovated.
.Goguryeo Fortresses in North Korea and China
.Of the numerous mountain fortresses built by Goguryeo, various remains can be found scattered about North Korea and northeast China. However, it is not known just how many Goguryeo mountain fortresses remain in China. There are dozens in North Korea, including Pyeong-yang’s Daeseongsanseong Fortress and Baengmasan-seong Fortress.
.Daeseongsanseong Fortress on Mt. Daeseongsan (height: 270 meters) nearby the city of Pyeongyang, North Korea extends about 7 kilometers in length. Upon its construction during the middle of the third century, it became highly significant, both politically and militarily, when the capital was relocated to Pyeongyang in 427. The fortress collapsed after the reign of Goguryeo, but remnants of the fortress gate, reservoir, food storage facilities, barracks, and armories still remain. Anhakgung Palace, located to the south of Daeseongsanseong Fortress, was housed within a royal palace fortress that encompassed a length of about 2.5 kilometers built on flat terrain. This arrangement of fortress facilities of Pyeongyang was modeled after Gungnaeseong Fortress of the former capital area.
.Baengmasanseong Fortress is located on Mt. Baengmasan (height: 410 meters) in Pyeonganbuk-do province, North Korea. It was first built during the Goguryeo period but was continuously maintained and operated through the Joseon period. It consists of a 2.6-kilometer-long inner wall and 2.4-kilometer-long outer wall, both about 6 meters in height. The inner and outer walls both included four arched gates. The fortress was situated at an especially strategic location on the border with China where the Korean peninsula connects with the Asian continent. In particular, it provided a clear view in all directions and thus was ideal for observing enemy movements and cutting off routes of retreat. Qing armies attacked the fortress but were unable to capture it.
.As for Goguryeo mountain fortresses in present-day China, some 100 fortresses can be found in the areas of Jilin Province and Liaoning Province. However, it is believed that a much greater number was actually built in China by Goguryeo. Representative Guguryeo mountain fortresses include Onyeosanseong Fortress in Huanren, Sanseongjasanseong Fortress, Bonghwansanseong Fortress, and Yeonjuseong Fortress, all of which are familiar to South Koreans.
.Onyeosanseong Fortress is said to be the first fortress built by Goguryeo founder King Dongmyeong after the founding of his nation. A monument to King Gwanggaeto cites that he “uilt a fortress and founded a city on the mountain west of Holbon in Biryugok Valley,”while Samguksagi (History of the Three Kingdoms) also includes references to the fortress. Onyeosanseong Fortress was built on a vast plateau, measuring 1,000 meters north to south and 300 meters east to west, high up the cliffs of Mt. Onyeosan (height: 820 meters). Even at this high elevation, water was relatively plentiful, while precipitous cliffs on three sides provided a natural deterrence against invaders.Yeonjuseong Fortress was known as Baegamseong Fortress during the Goguryeo period. It was built on a mountain slope along the Taizihe River, with a sheer cliff on its east side facing the river. It is the most representative example of Goguryeo’s advanced fortress construction techniques, as highlighted by its massive fortress walls and the magnificence of its elaborately constructed bastions. A fierce battle was fought here when Tang China invaded Goguryeo in 645. After emerging victorious, the Tang king pressed on to Ansiseong Fortress, but Goguryeo troops resisted the siege for three months and eventually fended off the Tang forces.