Rare Empty Letter Sent by a Former Polish Prisoner in Spanish Concentration Camp to a Relative 1942. Most probably this Pole was captured by National army of Francisco Franco during the Spanish Civil War because he was a member of the communist International Brigades created by Stalin to fight the Nationalists. Envelope has censorship ink stamp. The concentration camp was the most important one in Franco's Spain, the Camp of Miranda de Ebro in Burgos region. Letter is missing. Rare .