states of Europe, has probably introduced the custom of keeping, in all neighbouring countries, ambassadors or ministers constantly resident, even in the time of peace. This custom, unknown to ancient times, seems not to be older than the end of the fifteenth, or beginning of the sixteenth century; that is, than the time when commerce first began to extend itself to the greater part of the nations of Europe, and when they first began to attend to its interests.
It seems not unreasonable, that the extraordinary expense which the protection of any particular branch of commerce may occasion, should be defrayed by a moderate tax upon that particular branch; by a moderate fine, for example, to be paid by the traders when they first enter into it; or, what is more equal, by a particular duty of so much per cent. upon the goods which they either import into, or export out of, the particular countries with which it is carried on. The protection of trade, in general, from pirates and freebooters, is said to have given occasion to the first institution of the duties of customs. But, if it was thought reasonable to lay a general tax upon trade, in order to defray the expense of protecting trade in general, it should seem equally reasonable to lay a particular tax upon a particular branch of trade, in order to defray the extraordinary expense of protecting that branch.