The organization of underground resistance movements in Auschwitz began in the second half of 1940, shortly after the camp became operational in May of that year. In September 1940 rotmistrz Witold Pilecki arrived in the camp. Pilecki (using the name Tomasz Serafiński, prisoner number 4859) had allowed himself to be captured by Germans in a street round up (łapanka) with the specific purpose of having himself sent to Auschwitz in order to gather information on the then new camp, and to organize resistance inside. Under Pilecki's direction the Związek Organizacji Wojskowej (Union of Military Organization), ZOW, was formed.
After the western part of the country was annexed by Nazi Germany during the Nazi-Soviet invasion of Poland, Oświęcim (Auschwitz) was located administratively in the German Province of Upper Silesia, Regierungsbezirk Kattowitz. Auschwitz was first suggested as the location of a concentration camp for Polish nationals by SS-Oberführer Arpad Wigand, an aide to Higher SS and Police Leader for Silesia, Erich von dem Bach-Zelewski. Bach-Zelewski had been searching for a new site to intern people in the Silesia region because the local prisons were filled to capacity. Richard Glücks, head of the Concentration Camps Inspectorate, sent former Sachsenhausen concentration camp commandant Walter Eisfeld to inspect the site, which already held sixteen dilapidated one-story buildings that had once served as an Austrian and later Polish Army barracks.Reichsführer-SS Heinrich Himmler, head of the Schutzstaffel (SS), approved the site in April 1940, intending to use the facility to house political prisoners. SS-Obersturmbannführer (lieutenant colonel) Rudolf Höss oversaw the development of the camp and served as the first commandant. SS-Obersturmführer (senior lieutenant) Josef Kramer was appointed Höss's deputy. Auschwitz I, the original camp, became the administrative center for the whole complex.