The Hansaviertel is a small locality (the smallest one among the 95 Berliner Ortsteile) between Großer Tiergarten park and the Spree river within the central Mitte borough of Berlin. It was almost completely destroyed during World War II, but was rebuilt from 1957 to 1961 as a housing estate project by international master architects like Alvar Aalto, Egon Eiermann, Walter Gropius, Oscar Niemeyer, Sep Ruf etc., called Interbau. The whole ensemble, including two churches (St. Ansgar and Kaiser-Friedrich-Gedächtniskirche), is now protected as a historic monument.