The 4-dollar Columbian Exposition Issue was the first U.S. stamp to bear the portrait of a woman, Queen Isabella of Spain. Isabella of Castile married Ferdinand of Aragon in 1469, thus uniting their two kingdoms. They spent most of the years of their union fighting to expel the Moors from the southern reaches of the Iberian Peninsula, a feat accomplished in 1492. In the same year she agreed to finance Christopher Columbus's expedition of discovery. That same year she moved to purge the nation of Sephardic Jews in what became known as the 'Spanish Inquisition'.
After the 4-dollar stamp's 1893 debut, women of social and political significance slowly gained recognition on stamps. Martha Washington, wife of the country's first president, was honored on a 1902 postage stamp. Then in 1907, the Indian princess Pocahontas was featured on a 5-cent stamp to memorialize her contribution to peace in the early Virginia colony. In 1936 a stamp honored Susan B. Anthony for her work in the woman suffrage movement.
Stamp collectors and dealers who saw the opportunity to create collectible covers used the 4-dollar stamp to drastically overpay the usually low-value domestic rates. But in a few cases, it paid expensive heavyweight foreign destination rates. American Bank Note Company printed a total 26,350 stamps of this issue.