《资治通鉴·晋纪·晋纪三十四》
北魏博士李先说： 兵法云：驻军在高的地方，就要被敌人围困；驻军在地势低洼的地方，就要被敌人囚禁。
魏博士李先曰： 兵法：高者为敌所栖，深者为敌所囚。
Physician Li Xian of the Northern Wei state said: The art of war says: If you garrison on a high place, you will be besieged by the enemy; if you garrison on a low place, you will be captured by the enemy.