Auschwitz Concentration Camp opened in former Polish army barracks in June 1940. Twenty brick buildings were adapted, of which 6 were two-story and 14 were single-story. At the end of 1940, prisoners began adding second stories to the single-story blocks. The following spring, they started erecting 8 new blocks. This work reached completion in the first half of 1942. The result was a complex of 28 two-story blocks, the overwhelming majority of which were used to house prisoners. As a rule, there were two large rooms upstairs and a number of smaller rooms downstairs. The blocks were designed to hold about 700 prisoners each after the second stories were added, but in practice they housed up to 1,200.