清川江
When Sui army had reached Salsu (thought to be the present-day Chongchon River), Goguryeo charged the remaining Sui army. Eulji Mundeok defended fortresses against the Sui army and navy for several months and destroyed the Sui troops while retreating into Goguryeo territory. An attack at Salsu (Chongchon River) inflicted massive casualties on the Sui forces. When the Sui army had reached Salsu, Eulji Mundeok's force slaughtering them. The historical text records that Sui soldiers had to run almost 200 km that day to escape death. The Battle of Salsu contributed to the massive overall casualty figure for Sui during the campaign. Emperor Yang crossed the Liao River to attack Goguryeo. Of the initial 305,000 men, only 2,700 returned.