 The most important source for potential locations is the so-called "Judenkartei" (Jews register), which was set up at the 1939 census of Germany as of 17 May 1939.In cases where the actual houses were destroyed during World War II or during later restructuring of the cities, some "Stolpersteine" have been installed at the former site of the house.By the end of 2016, Gunter Demnig and his co-workers had installed about 60,000 stones in more than 1,200 towns and cities throughout Europe