King Kwanggaetho is the 17th descendant of King Tongmyong, founder of Koguryo (277 BC-AD 668). His name was Tamdok, and he reigned for 22 years from 391 to 412. He became a crown prince in 386, and ascended the throne in 391 and actively pushed ahead with the policy of southward advance that had been pursued by Koguryo.
In 391, in order to check the invasion by Japan that was in league with Paekje and Kaya, Kwanggaetho attacked and defeated Paekje by sea. From 392 to 395 he waged several battles and occupied over ten fortresses of Paekje, including Sokhyon Fortress, the country's northern bulwark, and Kwanmi Fortress.
In 396 he attacked Paekje by dint of land and sea forces, dashing into its capital and accepting its king's surrender. And he turned Silla into his country's inferior ally in 392. In 400, at the request of Silla, he dispatched 500-strong infantry and cavalry forces to assault troops of Paekje and Kaya and their subordinate ally Japan, dealing a severe blow to the states.
In 404 he won a great victory by annihilating innumerable Japanese troops, and in 407 defeated Paekje once again. From 391 to 395 he punished and subdued Piryo tribe of the Khitai who had been menacing the northwest border of Koguryo, and attacked Yan dynasty (Later Yan), which had invaded the country several times, to frustrate its attempt of aggression. In 407 he improved relations with north Yan.
In 410 he attacked east Puyo northeast of his country, occupying and subjugating 64 fortresses and 1 400 villages.
As a result, Koguryo, during the period of his reign, became the strongest country in the Orient.
As to domestic affairs, he vigorously pushed ahead with the construction of the Walled City of Pyongyang, including the building of nine temples in the city in 393.
As the king of feudal state he pursued anti-popular policies to intensify repression and exploitation of the people. He, however, made a contribution to strengthening the might of the country in no small measure by expanding its territory and making great progress in unifying the three states—Koguryo, Paekje and Silla.
His personal history and achievements are inscribed in detail on the Monument to the Mausoleum of King Kwanggaetho in Jian, Jilin Province, China.
The epitaph on the monument is divided mainly into three paragraphs.
The first paragraph, as preface, describes how King Tongmyong founded Koguryo, succession of the following kings to the throne, a general review of King Kwanggaetho's feats and why the mausoleum and the monument were erected.
The second describes King Kwanggaetho's feats by year and event. The description includes the fact that the king punished Piryo tribe, Siksin tribe and east Puyo on the north, demonstrating the prestige of the country and expanding its territory, and the fact that on the south, he dealt a decisive blow to Paekje, Kaya and Japan, occupying many of Paekje's fortresses, and helped and put Silla under its stronger control, demonstrating the might of his country and expanding its territory.
The third describes the formation of a grave keepers' group to manage and protect the mausoleum and the provisions of an act to permanently maintain the group. Therefore the monument can be said to be the one to the king's achievements and the one to the act on the principles for keeping the mausoleum.
The epitaph contains details of many facts never found in historical records at home and abroad. Thus it serves as indispensable fundamental data for having a correct understanding of and systematizing the history of Koguryo and that of the Orient.
The epitaph consists of excellent compositions engraved on the basis of outstanding calligraphy, and the monument is a magnificent natural rock trimmed enough to be inscribed with characters. It shows the extent to which Koguryo people's aesthetic taste developed.
As one of the oldest inscribed monuments in Korea, the monument is regarded as the nation's precious cultural heritage for its valuable historical data with rich content, its imposing appearance and the liberal style of the characters.