Gen. Sal Ye-t‘ap had gone north and joined another division of the Mongol army and again he attacked Ku-ju. He made engines of war called _ta-p‘o-ch‘a_, a sort of catapult, with which to reduce this town, but the magistrate, Pak Sö also made similar instruments which hurled huge stones, and the besiegers were compelled to retire to a distance and take refuge behind various kinds of defenses. The Mongols made three attempts to deceive the prefect by forged letters purporting to be from the king and saying “I have surrendered and therefore you must submit,” but Pak Sö was not to be caught by so simple a trick. The besiegers then tried huge scaling ladders, but these were cut down by the defenders as fast as they were put in place. An aged Mongol general, who made a circuit of the town and marked the splendid state of defense into which the place had been put, declared that he had never seen a place so well defended.
So the little town stood and the great Mongol general was forced to seek other fields for the display of his prowess. He sent a letter to the king finding fault because of the death of the first Mongol messenger and modestly suggesting that peace could be secured if he would surrender and give 20,000 horse-loads of clothing, 10,000 pieces of purple silk, 20,000 sea-otter skins, 20,000 horses, 1,000 boys, 1,000 girls and 1,000,000 soldiers, with food, to help conquer Japan. In addition to this the king must go to the Mongol court and do obeisance. These were the terms upon which Koryŭ could secure peace.
With the beginning of the next year, 1232, the king sent two generals bearing a letter of surrender. With it he sent seventy pounds of gold, thirteen pounds of silver, 1,000 coats and a hundred and seventy horses. He moreover stated that the killing of the Mongol messenger was not the work of the Koryŭ government but of a band of insurgents and robbers. The officials had to give their garments in order to make up the number that was sent. Each prefect along the route was charged with the duty of seeing that the Mongols were in no way molested.
But Pak Sö the prefect of Ku-Ju was an obstinate man and would not give up his fortress even when he knew the king had surrendered. It was only after a great deal of argument and expostulation that he at last capitulated. The Koryŭ people wanted to kill him for his obstinacy but the Mongols said “He is your greatest man and you should prize him highly.”