The Wealth of Nations by Part 5 Chapter 1 Page 120

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