Auschwitz-Birkenau was the largest of Nazi Germany's concentration camps and extermination camps, operational during World War II.
The camp took its German name from the hosting town of Oświęcim. Following the German invasion of Poland in September 1939, Oświęcim was annexed by Nazi Germany and renamed Auschwitz, the town's German name. Birkenau, the German translation of Brzezinka (birch tree), refers to a small Polish village nearby which later was mostly destroyed by the Germans.
The camp commandant, Rudolf Höss, testified at the Nuremberg Trials that up to 3 million people had died at Auschwitz. The Auschwitz-Birkenau State Museum has revised this figure to 1.1 million, about 90% of whom were Jews from almost every country in Europe. Most victims were killed in Auschwitz II's gas chambers using Zyklon B; other deaths were caused by systematic starvation, forced labor, lack of disease control, individual executions, and purported "medical experiments".
In 1947, in remembrance of the victims, Poland founded a museum at the site of the first two camps. By 1994, some 22 million visitors - 700,000 annually - had passed through the iron gate crowned with the motto Arbeit macht frei (Work brings freedom). The anniversary of the liberation of Auschwitz by Soviet troops on January 27, 1945 is celebrated on International Holocaust Remembrance Day, Holocaust Memorial Day in the United Kingdom, and other similar memorial days in various countries.