In early 1937, the SS, using prisoner labor, initiated construction of a large complex of buildings on the grounds of the original camp. The construction was officially completed in mid-August 1938 and the camp remained essentially unchanged and in operation until 1945. A crematorium that was next to, but not directly accessible from within the camp, was erected in 1942. KZ Dachau was therefore the longest running concentration camp of the Third Reich. The Dachau complex included other SS facilities beside the concentration camp—a leader school of the economic and civil service, the medical school of the SS, etc. The camp at that time was called a "protective custody camp," and occupied less than half of the area of the entire complex.
Dachau, located ten miles north of Munich, Germany, was the first concentration camp built by the Nazis and served as a model for all later camps. By 1937, it held 13,260 prisoners, including German communists and social democrats as well as Jehovah’s Witnesses, Roma (Gypsies), and homosexuals. Dachau also served as the central camp for Christian religious prisoners.
The mass killings of Jews in the occupied Soviet territories were assigned to four SS formations called Einsatzgruppen ("task groups"), which were under Heydrich's overall command. Similar formations had been used to a limited extent in Poland in 1939, but the ones operating in the Soviet territories were much larger. The Einsatzgruppen's commanders were ordinary citizens: the great majority were professionals and most were intellectuals. By the winter of 1941–1942, the four Einsatzgruppen and their helpers had killed almost 500,000 people. The largest massacre of Jews by the mobile killing squads in the Soviet Union was at a ravine called Babi Yar outside Kiev, where 33,771 Jews were killed in a single operation on 29–30 September 1941.[n] A mixture of SS and Security Police, assisted by Ukrainian police, carried out the killings. Although they did not actively participate in the killings, men of the German 6th Army helped round up the Jews of Kiev and transport them to be shot. By the end of the war, around two million are thought to have been victims of the Einsatzgruppen and their helpers in the local population and the German Army. Of those, about 1.3 million were Jews and up to a quarter of a million Roma.
Auschwitz, perhaps the most notorious and lethal of the concentration camps, was actually three camps in one: a prison camp (Auschwitz I), an extermination camp (Auschwitz II–Birkenau), and a slave labour camp (Auschwitz III–Buna-Monowitz). Upon arrival, Jewish prisoners faced what was called a Selektion. A German doctor presided over the selection of pregnant women, young children, the elderly, handicapped, sick, and infirm for immediate death in the gas chambers. As necessary, the Germans selected able-bodied prisoners for forced labour in the factories adjacent to Auschwitz, where one German company, IG Farben, invested 700 million Reichsmarks in 1942 alone to take advantage of forced labour, a capital investment. The conglomerate presumed that slave labour would be a permanent part of the German economy. Deprived of adequate food, shelter, clothing, and medical care, these prisoners were literally worked to death. Periodically, they would face another Selektion. The Nazis would transfer those unable to work to the gas chambers of Birkenau.
The camp was liberated on April 15, 1945, by the British 11th Armoured Division. The soldiers discovered approximately 60,000 prisoners inside, most of them half-starved and seriously ill, and another 13,000 corpses, including those of Anne and Margot Frank, lying around the camp unburied. The horrors of the camp, documented on film and in pictures, made the name "Belsen" emblematic of Nazi crimes in general for public opinion in many countries in the immediate post-1945 period. Today, there is a memorial with an exhibition hall at the site.