Unusual rock formation of Lookout Mountain in Chattanooga, Tennessee. It appears perilously balanced; but more than thirty people can stand on its top at one time. A postcard is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. Postcards were made because people were looking for an easier way to send quick notes. Postcards, in the form of government postal cards and privately printed souvenir cards, became very popular as a result of the Columbian Exposition, held in Chicago in 1893, after postcards featuring buildings were distributed at the fair.