During the World War II Nazi occupation, Fort VII gained notoriety as a Nazi concentration camp, where up to 20,000 Poles died. Between 1940 and 1945, Fort Grolman and Fort Rauch formed the nucleus of the Stalag XXI-D PoW camp. In the later part of the war Poznań was declared one of the stronghold cities ("Festungen") which the Nazis intended to defend at all costs, and so the name "Festung Posen" was revived. The outer forts were used to defend the city during the Battle of Poznań (1945), and Fort Winiary was the defenders' last point of resistance, the reduit incurring significant damage. After the war the site of Fort Winiary was converted into the Cytadela park.