Auschwitz and Birkenau were separated from each other by about a 45-minute walk. Auschwitz was adapted to hold political prisoners in 1940 and evolved into a killing machine in 1941. Later that year a new site called Birkenau was found to extend the Auschwitz complex. Here a vast complex of buildings were constructed to hold initially Russian POWs and later Jews as a labour pool for the surrounding industries including IG Farben. Following the January 1943 Wannsee Conference, Birkenau evolved into a murder factory using makeshift houses which were adapted to kill Jews and Russian POWs. Later due to sheer volume Birkenau evolved into a mass killing machine using gas chambers and crematoria, while Auschwitz, which still held prisoners, became the administrative centre.