The Republic of Panama has been a member of the Universal Postal Union since 1904. The history of mail began in the 19th century, when Panama was one of the states of Colombia (1830 - 1903). In 1878, a series of four stamps with the image of the Isthmus of Panama and the inscriptions “CORREOS E. S. DE PANAMA” (“Post of the Sovereign State of Panama”) and (“United States of Colombia”) entered postal circulation especially for Panama. The stamps were lithographically printed on both thin and thick paper. The stamps from this issue are considered to be the first postage stamps of Panama. Since 1887, overprinted Colombian postage stamps have been used in the state of Panama.