Auschwitz I (German name for Oświęcim) was the original camp, serving as the administrative center for the whole complex as it grew. On September 3, 1941, deputy camp commandant SS-Hauptsturmführer Fritzsch experimented on 600 Russian POWs and 250 Polish inmates by gathering them in the basement of Block 11 and gassing them with Zyklon B, a highly lethal cyanide-based pesticide. This paved the way for the use of Zyklon B as an instrument for extermination at Auschwitz, and a gas chamber and crematorium were constructed by converting a bunker. This gas chamber operated from 1941 to 1942, during which time some 60,000 people were killed therein.
Although the Auschwitz I site remains the symbol of the holocaust in popular culture with its famous “Arbeit macht frei” (Work sets you free) sign above the entrance gate and the fact that industrialised murder was developed in the camp the majority of the killing (approximately 90%) took placed in the purpose constructed extermination camp at Auschwitz II Birkenau a few miles from Auschwitz I.