Now that the fortunes of Koryŭ were manifestly in the ascendant, many people in the north sent and swore allegiance to her, thus following the example of a certain Kitan envoy who at this time transferred his citizenship voluntarily from Kitan to Koryŭ.
The King died and his son Heum, posthumous title Tŭk-jong, came to the throne in 1032. He married his own sister. All friendly relations with Kitan were broken off, because the bridge across the Yalu was not destroyed. It did not seem a friendly act to leave this standing menace to the peace of Koryŭ. In view of this the King ordered a wall to be built across the entire peninsula from the Yalu River to the Japan Sea. It was nearly a thousand _li_ long. This would seem almost incredible were it not that the facts are given in such detail. The wall was twenty-five _cha_ high and the same in breadth and stretched from Ko-gung-nă Fortress, near Eui-ju on the Yalu, to Yöng-heung near the Japan Sea. The Kitan people tried to hinder this work but without avail. This period marks the acme of Koryŭ’s power and wealth. She had reached her zenith within a century and a quarter of her birth and now for three centuries she was destined to decline.
The younger brother, Hyöng, of this King Tŭk-jong, succeeded him in 1035, after a short reign of three years. He continued the work of making impregnable the defenses of the north. He built a wall from Song-ryŭng Pass in the west to the borders of the Yŭ-jin tribe in the north-east. He also built a Fortress Chă-jŭn, now Ch‘ang-sŭng. His reign beheld the riveting of Buddhistic chains upon the kingdom. Those who could read the signs of the times surmised this when, in 1036, the King decreed that, if a man had four sons, one of them must become a monk. Because of the Buddhistic canon against the spilling of blood the death penalty was commuted to banishment. Another Buddhistic anniversary was instituted. The King also inaugurated the custom of having boys go about the streets bearing Buddhistic books upon their backs from which the monks read aloud as they passed along. This was for the purpose of securing blessings for the people.
In order to counteract the tendency toward luxury, the King forbade the use of silk and gold and went so far as to burn up the whole stock of silk held by the merchants. He made a new law of primogeniture. The first son is to succeed. If he dies, the son of the first son succeeds. If there is no grandson the second son succeeds. If there is no son by the wife the son by a concubine succeeds. If there is none then a daughter succeeds. The Yŭ-jin tribe came with rich gifts and promised faithfully to refrain from raiding the frontier again. In 1047 the King was succeeded by his younger brother, Whi, posthumous title Mun-jong, who was destined to sit upon the throne for thirty-seven years. After announcing to his suzerain his accession, he followed the custom of his house and married his sister.