《明史·志·卷五十六》
到安南新来归附，粮饷更加难以为继，于是各所又招来商人轮粮以换盐，别的边地又依次实行。
迨安南新附，饷益难继，於是诸所复召商中盐，他边地复以次及矣。
When the newly-subdued people in Annam arrived, grain and money were hard to sustain, so various places recruited merchants to exchange grain for salt, and other border areas implemented the same one after another.