The rainy season had now come and gone and the main plan of the invasion was ready to be worked out. It was necessary for the Emperor to spread out his force over the country in order to find forage, and so, in approaching the borders of Ko-gu-ryŭ, it was decided that they should come by several different routes. Gen. U Mun-sul led a detachment by way of Pu-yŭ, Gen. U Chung-mun by way of Nang-nang, Gen. Hyŭng Wŭn-hang by way of Yo-dong, Gen. Sŭl Se-ung by way of Ok-jŭ, Gen. Sin Se-ung by way of Hyŭn-do, Gen. Chang Keun by way of Yang-p’yăng, Gen. Cho Hyo-jă by way of Kal-sŭk, Gen. Ch’oe Hong-seung by way of Su-sung, Gen. Wi Mun-seung by way of Cheung-ji. It is said that they all rendezvoused on the western bank of the Yalu River, but if so there must have been great changes in the position of these wild tribes. It is more than probable that like the North American Indians they had moved further and further back from their original lands until they were far beyond the Yalu and Tumen rivers.
In the early autumn of 612 the whole army lay just east of the Yalu River.
The king of Ko-gu-ryŭ sent Gen. Eul-ji Mun-dŭk to the Chinese camp to tender the Emperor a pretense of surrender but in reality to spy out his position and force. When he appeared the Emperor was minded to kill him on the spot but thought better of it and, after listening to what he had to say, let him go. Not an hour after he had gotten beyond the Chinese pickets the Emperor changed his mind again and sent in pursuit of him; but the general had too good a start and made too good use of his time to allow himself to be retaken.
And now appeared one of the disadvantages of being far from one’s base of supplies, and in an enemy’s country. Some weeks before this each Chinese soldier had been given three bags of rice and told that he must carry them on the march, besides his other necessary accoutrements. Death was to the penalty of throwing any of it away. The result was that most of them buried a large part of the rice in their tents and so escaped detection. Now they were short of provisions, while the generals thought their knapsacks were full of rice. The Ko-gu-ryŭ Gen. Eul-ji, who had been in their camp, however, knew about it. He entered upon a geurilla warfare with the object of luring the enemy far into Ko-gu-ryŭ territory and then cutting them to pieces at leisure. To this end he made a feigned retreat several times each day, thus giving the enemy confidence and blinding them to his own strength. It was decided that a Chinese force of 305,000 men under Gen. U Chung-mun should proceed straight to P’yŭng-yang. It seemed wholly unnecessary that the whole army of 1,130,000 men should undergo that long march when only a pusillanimous enemy barred the way.