As the mountainous area is mostly on the eastern part of the peninsula, the main rivers tend to move westwards. Two exceptions tend to be the southward-flowing Nakdong River and Seomjin River.
Although the Sui army was lured into a entice because of the famed Koguryŏ commander Ŭlchi Mundŏk, and endured a calamitous defeat on the Salsu (Ch'ŏngch'ŏn) River. It is claimed that only two,700 on the 300,000 Sui troopers who had crossed the Yalu survived to discover their way back, as well as Sui emperor now lifted the siege of Liao-tung Fortress and withdrew his forces to China suitable. Yang Ti continued 토토 to send his armies versus Koguryŏ but all over again with no achievement, and right before extended his war-weakened empire crumbled." ^