Natzweiler-Struthof was the only camp established on French territory (although the Nazis considered this conquered Alsace region of French to be part of greater Germany). It was located not far from Strasbourg and was in operation from April 1941 to liberation in November 1944. During this period, a total of 52,000 were interned; some 22,000 of them died. The camp held the usual mixture of jews, gypsies, homosexuals, and Nacht und Nebel (Night and Fog) political prisoners. In 1943, a gas chamber was set up to study new gases and provide skeletons to the Nazi professors at the Reich University of Strasbourg. 86 jewish victims were gassed in this macabre facility. The Nazis had hoped to use plaster casts of the skeletons to prove their racial superiority theories, but had to dispose of the corpses as the Allied forces approached.  Link.