Twenty countries have participated in events commemorating the murder of 150000 people here during the Second World War, one-third of whom were Jewish. Mauthausen was classified by the SS administration as a “Category 3” camp; this category of camp corresponded to the harshest possible treatment. The prisoners sent here were designated “return undesirable” and destined for “extermination through work”. All activities in the camp gravitated around the stone quarry and the construction of tunnels in the infamous adjoining camp of Gusen, Melk, and Ebensee. The Mauthausen camp was liberated on 5 May 1945 by the American Eleventh Armored Division. A memorial ceremony takes place every year on that date.