《明史·志·卷五十一》
凡是在京外各府州县关隘渡口等要害处都设立，使他们率领兵士役夫警戒防备不测。
凡在外各府州县关津要害处俱设，俾率徭役弓兵警备不虞。
They were established in all key places such as gates and passes outside of the capital in various prefectures, states, and counties. They led soldiers and servants to be vigilant and prevent any accidents.