The world’s longest residential building, Karl Marx-Hof, is located in the neighbourhood of Heiligenstadt in the Austrian capital city of Vienna. Built between 1927 and 1930 by city planner Karl Ehn, the colossal building is 1,100 meters long – a length spanned by four tram stops and interspersed by several tunnels that had to be incorporated into the design to allow the continuation of city streets and traffic flow. It was one of the approximately 400 new municipal apartment complexes, called Gemeindebauten, built by the Social Democrats to provide housing to the thousands of families rendered homeless after the First World War.

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