The first 3 issues of U.S. Revenues are some of the most beautifully engraved stamps ever issued by the U.S. These stamps were used between 1862 and 1874, to pay taxes to the U.S. Government on documents and proprietary articles.
The first series, which interests me the most, is comprised of many more stamps than the second and third issues. There are four main "varieties" of each denomination/type (not every type existed in every variety):