Following the German invasion of Poland in September 1939 , Fort VII was chosen as the site of the first concentration camp in occupied Poland , called '' Konzentrationslager Posen '' . It was probably created by decision of the '' Reichsstatthalter '' of the Poznań region , Arthur Greiser . It began functioning at some time around October 1939 . The prisoners were mostly Poles from the Wielkopolska region . Many were representatives of the region 's intelligentsia , often people who had been engaged in social and political life , as well as known Polish patriots and veterans of the Wielkopolska Uprising ( 1918 – 1919 ) and Silesian Uprisings . In the early stages of the camp 's existence prisoners were generally executed within a week of arrival . In October 1939 an early experiment in execution by gas chamber was carried out by an SS chemist , Dr. August Becker , p. 175 whereby around 400 patients and staff from psychiatric hospitals in Poznań were gassed at Bunker No. 17 . The extermination of mentally ill was conducted by '' SS-Sturmbannführer '' Herbert Lange , chief of the Gestapo in occupied Poznań . Lange served with '' Einsatzgruppe '' VI during Operation Tannenberg . He and his men were responsible also for the murder of 2,750 patients at Kościan , about 1,100 patients at Owińska , as well as 1,558 patients and 300 civilian Poles at Działdowo ; the experience gained allowed Lange to become the first commandant of Chełmno extermination camp ( until April 1942 )
Operation Tannenberg
Operation Tannenberg
Fort VII