1941 – World War II: The first gas chamber experiments are conducted at Auschwitz
. Auschwitz concentration camp was a network of German Nazi concentration camps and extermination camps built and operated by the Third Reich in Polish areas annexed by Nazi Germany during World War II. It consisted of Auschwitz I (the original camp), Auschwitz II–Birkenau (a combination concentration / extermination camp), Auschwitz III–Monowitz, and 45 satellite camps. Auschwitz I was first constructed to hold Polish political prisoners, who began to arrive in May 1940. The first extermination of prisoners took place in September 1941, and Auschwitz II–Birkenau went on to become a major site of the Nazi "Final Solution to the Jewish question." From early 1942 until late 1944, transport trains delivered Jews to the camp's gas chambers from all over German-occupied Europe, where they were killed with the pesticide Zyklon B. At least 1.1 million prisoners died at Auschwitz, around 90 percent of them Jewish; approximately 1 in 6 Jews killed in the Holocaust died at the camp. Others deported to Auschwitz included 150,000 Poles, 23,000 Romani and Sinti, 15,000 Soviet prisoners of war, 400 Jehovah's Witnesses, homosexuals, and tens of thousands of people of diverse nationalities. Living conditions were brutal, and many of those not killed in the gas chambers died of starvation, forced labor, infectious diseases, individual executions, and medical experiments.