Plans for the total eradication of the Jewish population of Europe—eleven million people—were formalised at the Wannsee Conference, held on 20 January 1942. Some would be worked to death, and the rest would be killed in the implementation of the Final Solution of the Jewish question (). Permanent killing centres at Auschwitz, Belzec, Chelmno, Majdanek, Sobibor, Treblinka, and other Nazi extermination camps replaced mobile death squads as the primary method of mass killing. The "Einsatzgruppen" remained active, however, and were put to work fighting partisans, particularly in Belarus.