The Gusen concentration camp began construction in December 1939 and officially opened on 25 May 1940, with the arrival of over 1,000 Polish prisoners. From the start, it was part of the SS’s plans for the economic exploitation of the granite quarries in the region through the forced labour of concentration camp prisoners. The camp held a special position within the system of concentration camps named after its main camp, Mauthausen, which included over 40 subcamps. More than a subcamp, Gusen was considered a twin camp to Mauthausen.