The Auschwitz concentration camp (Konzentrationslager Auschwitz) was a complex of over 40 concentration and extermination camps built and operated by Nazi Germany in occupied Poland during World War II and the Holocaust. It consisted of Auschwitz I, the main camp (Stammlager) and administrative headquarters, in Oświęcim; Auschwitz II–Birkenau, a combined concentration/extermination camp three kilometers away in Brzezinka; Auschwitz III–Monowitz, a labor camp seven kilometers from Auschwitz I, set up to staff an IG Farben synthetic-rubber factory; and dozens of other subcamps.After Germany invaded Poland in September 1939, sparking World War II, the Germans converted Auschwitz I from an army barracks to hold Polish political prisoners. The first prisoners, German criminals brought to the camp as functionaries, arrived in May 1940, and the first gassing of prisoners took place in block 11 of Auschwitz I in September 1941. Auschwitz II–Birkenau went on to become a major site of the Nazis' Final Solution to the Jewish Question. From early 1942 until late 1944, transport trains delivered Jews from all over German-occupied Europe to the camp's gas chambers. Of the estimated 1.3 million people sent to Auschwitz, at least 1.1 million died, around 90 percent of them Jews. Approximately one in six Jews killed in the Holocaust died at the camp. Others deported to Auschwitz included 150,000 non-Jewish Poles, 23,000 Roma, 15,000 Soviet prisoners of war, 400 Jehovah's Witnesses, tens of thousands of others of diverse nationalities, and an unknown number of gay men. Many of those not killed in the gas chambers died because of starvation, forced labor, infectious diseases, individual executions, and medical experiments. In the course of the war, the camp was staffed by 7,000 members of the German Schutzstaffel (SS), approximately 12 percent of whom were later convicted of war crimes. Several, including camp commandant Rudolf Höss, were executed. The Allies did not act on early reports of atrocities at the camp, and their failure to bomb the camp or its railways remains controversial. At least 802 prisoners tried to escape from Auschwitz, 144 successfully, and on 7 October 1944 two Sonderkommando units, consisting of prisoners assigned to staff the gas chambers, launched a brief, unsuccessful uprising. As Soviet troops approached Auschwitz in January 1945, most of its population was sent west on a death march. The remaining prisoners were liberated on 27 January 1945, a day commemorated as International Holocaust Remembrance Day. In the following decades, survivors such as Primo Levi, Viktor Frankl, and Elie Wiesel wrote memoirs of their experiences in Auschwitz, and the camp became a dominant symbol of the Holocaust. In 1947 Poland founded the Auschwitz-Birkenau Memorial and Museum on the site of Auschwitz I and II, and in 1979 it was named a World Heritage Site by UNESCO.