The city of Oswiecim, renamed Auschwitz by the Third Reich, is home to the concentration camps established in 1940 and has become the symbol of genocide and the Holocaust. There are two camps here, the main camp known as "Auschwitz I" housed between 15,000 and 20,000 prisoners. The second camp, called Birkenau or "Auschwitz II," was the larger of the two camps and held more than 90,000 prisoners by 1944. It's difficult to know how many people died at Auschwitz. Some estimate about 500,000, while others think it's millions. But thousands of prisoners did survive and were witnesses to the crimes committed there, though some groups continue to deny the Holocaust ever happened. The camps reopened in 1955 and each year host more than a million visitors, who can bear witness to tragic events by way of photographs, artifacts and survivor stories.