Produced in conjunction with the 1898 Trans-Mississippi International Exposition, this set features themes of American westward expansion. The set is widely considered to include some of the finest engraving of any United States stamps, with vignettes based on the work of renowned artists including Frederick Remington. It was originally intended to be produced by a two color printing process, but the advent of the Spanish American War diverted stamp production resources to revenue stamps needed for the war effort and the stamps were issued in single colors. After a short 6-month period of availability, an unknown quantity of unsold Trans-Mississippi stamps were returned to the Post Office and destroyed.