Flossenbürg was a Nazi concentration camp built in May 1938 by the SS Main Economic and Administrative Office. Unlike other concentration camps, it was located in a remote area, in the Fichtel Mountains of Bavaria, adjacent to the town of Flossenbürg and near the German border with Czechoslovakia. The camp's initial purpose was to exploit the forced labor of prisoners for the production of granite for Nazi architecture. In 1943, the bulk of prisoners switched to producing Messerschmitt Bf 109 fighter planes and other armaments for Germany's war effort. Although originally intended for "criminal" and "asocial" prisoners, after Germany's invasion of the Soviet Union, the camp's numbers swelled with political prisoners from Eastern Europe. It also developed an extensive subcamp system that eventually outgrew the main camp.