The great Ch‘oe Chung-heun who had carried things with such a high hand now fell ill and died. This caused more commotion than the death of several kings. He was buried with royal honors. He left many sons, of whom U and Hyang were first and second. Hyang was a bold and powerful man, and before the father died he warned U against him. U succeeded to his father’s position which, as we have seen, corresponded closely with that of the Shogun of Japan. A serious rebellion broke out in the north under two leaders, Han Sun and Ta Chi, the cause being the illegal exactions of the prefects. When the king found that it could not be put down by peaceful means he sent Gen. Kim Ch‘ui-ro to put it down by force. The east Yŭ-jin leader, Myŭn Ku-ha, at first sided with the rebels but later changed his mind, invited Han Sun and Ta Chi to a feast, got them intoxicated, assassinated them, put their heads in a box and sent it to the king, thereby earning the good will of the latter. The king then reformed the abuses in the rebellious section and peace was at last secured. The Mongols were not to be content with an empty friendship, and in 1221 they sent a demand for revenue, consisting of 10,000 pounds of cotton, 3,000 rolls of fine silk, 2,000 pieces of gauze, 100,000 sheets of paper of the largest size. The envoy who brought this extraordinary letter was provided commodious quarters and excellent food but he expressed his dissatisfaction at everything by shooting arrows into the house posts, and by acting in a very boorish manner generally. The only man who could do anything with him was Kim Heui-jo who charged him with killing a man in Eui-ji, and threatened to have him imprisoned. Thus meeting bluster with bluster he made the brutal northerner listen to reason. When the envoy was about to go to an audience with his weapons in hand, this same Kim made him lay them aside. Other Mongol and Yo-jin messengers came and Kim managed them all so well that no trouble arose. It was becoming apparent that the Mongols were likely at any time to make a descent upon Koryŭ; so, in the following year, 1222, a wall was built near the Yalu river, extending from Eui-ju to Wha-ju. It is said that this was completed in the marvelously short space of forty days, a feat which shows not only how great a power Koryŭ could exert when necessary but how important she deemed it that this wall should be built.