In 1940, the Germany's Nazi government started to construct the Auschwitz and Groß-Rosen concentration camps. The latter camp provided labour for the construction of seven underground military facilities in the Owl Mountains and Książ Castle. Code-named Project Riese, work started in 1943 but was unfinished by the time Russian and Polish forces captured the area in 1945. An estimated 5,000 slave labourers died during the construction. Following Allied bombing of Silesian refineries and plants such as Blechhammer and Monowitz during the Oil Campaign of World War II, the synthetic plants and crude oil refineries [were neutralized] by the advance of the Russian armies c. February 20, 1945. In the January 1945 in Silesia the SS began marching approximately 56,000 prisoners in the Death marches out of the Auschwitz camps northwest to Gliwice and mostly west to Loslau (Polish: Wodzisław Śląski).