《资治通鉴·汉纪·汉纪一》
之所以派将领把守函谷关，是为了防备有其他盗贼出入和有非常情况发生。
所以遣将守关者，备他盗之出入与非常也。
The reason why I sent generals to guard Hangu Pass was to prevent other bandits from entering or leaving, and to deal with any emergencies.