In 1232 the Mongols increased their armies in the field, and attacked the Kins from two sides. Ogotai led the main force against Honan, while Tuli, marching through Shensi into Szchuen, assailed them on their western flank. The difficulties encountered by Tuli on this march, when he had to make his own roads, were such that he entered the Kin territories with a much reduced and exhausted army. The Kin forces gained some advantage over it, but by either a feigned or a forced retreat, Tuli succeeded in baffling their pursuit, and in effecting a junction with his brother Ogotai, who had met with better fortune. Tuli destroyed everything along his line of march, and his massacres and sacks revived the worst traditions of Mongol ferocity. In these straits the Kins endeavored to flood the country round their capital, to which the Mongols had now advanced, but the Mongols fell upon the workmen while engaged in the task, and slew ten thousand of them. When the main Kin army accepted battle before the town of Yuchow, it was signally defeated, with the loss of three of its principal generals, and Ninkiassu fled from Kaifong to a place more removed from the scene of war. The garrison and townspeople of Kaifong--an immense city with walls thirty-six miles in circumference, and a population during the siege, it is said, of one million four hundred thousand families, or nearly seven million people--offered a stubborn resistance to the Mongols, who intrusted the conduct of the attack to Subutai, the most daring of all their commanders. The Mongols employed their most formidable engines, catapults hurling immense stones, and mortars ejecting explosives and combustibles, but twelve months elapsed before the walls were shattered and the courage and provisions of the defenders exhausted. Then Kaifong surrendered at discretion, and Subutai wished to massacre the whole of the population. But fortunately for the Chinese, Yeliu Chutsai was a more humane and a more influential general, and under his advice Ogotai rejected the cruel proposal.