Throughout the 1930s and '40s, Nazis established thousands of concentration camps in Eastern Europe. In a small Polish town stands one of the most notorious and massive camps—Auschwitz. The complex spans 6,720 acres—almost half the size of Manhattan. Auschwitz consisted of three large subcamps: Auschwitz I, the torture center; Auschwitz II, or Birkenau, the point of arrival and main death factory; and Buna, the work camp.
In the beginning, prisoners were executed, starved or worked to death. Soon a faster method of killing evolved, allowing Nazis to murder thousands of people at a time—gas chambers.
Auschwitz was the Holocaust's most productive death camp. Seventy-five percent of those who arrived were immediately sent to the gas chambers, mostly women and children; the remaining were deemed fit to become slave laborers.
Based on declassified war-time intelligence reports, the Allies likely knew about the Nazis' plans to destroy Europe's Jews—as early as the summer of 1942. Nearly 5 million more Jews would be killed before the camps were finally liberated in 1945.