《隋书·列传·卷二十一》
这地方地势险要，且又低下潮湿。估计他们的人马，三天才能走完。即使我们慢慢地去追，何愁追不上？
贼若收军，必自蓼泉之北，此地险隘，兼复下湿，度其人马，三日方度，缓辔追讨，何虑不及？
This place is dangerous and humid. It is estimated that it will take three days for their horses and men to pass through. Even if we pursue them slowly, why worry about not catching up with them?