洮河
In order to avoid a costly frontal assault on the Song, which would have required a risky forced crossing of the lower Yangtze, Mongke decided to establish a base of operations in southwestern China, from which a flank attack could be staged. In the late summer of 1252 he ordered his brother Kublai to lead the southwest campaign. In fall, the Mongol armies advanced to the Tao River, then penetrated the Szechwan basin, defeated a Song army and established a major base in Sichuan. Total Mongol forces raised up to 100,000 men.