Since the mountainous area is mostly on the eastern A part of the peninsula, the primary rivers tend to move westwards. Two exceptions tend to be the southward-flowing Nakdong River and Seomjin River.
However the Sui Military was lured into a trap because of the famed Koguryŏ commander Ŭlchi Mundŏk, and endured a calamitous defeat at the Salsu (Ch'ŏngch'ŏn) River. It is alleged that only 2,seven-hundred on the 300,000 Sui troopers who had crossed the Yalu survived to find their way back again, and also the Sui emperor now lifted the siege of 슬롯 Liao-tung Fortress and withdrew his forces to China good. Yang Ti continued to send his armies from Koguryŏ but once more without accomplishment, and prior to extensive his war-weakened empire crumbled." ^