Walter Gropius. Ludwig Mies van der Rohe. Hugo Häring. Bruno Taut. Otto Rudolf Salvisberg. Erich Mendelssohn. Richard Neutra. Hans Poelzig. What a list! They all built here in the 1920s, when Berlin was the center of modernism. Come along on a tour that will show you why modern architecture was defined here. Just the magnificent forest settlement Onkel-Toms-Hütte by Taut or a subway with an attached shopping mall; a sensation back then. But don't think that the rich, conservative Zehlendorf would have waited for the world's revolutionaries. Steep roof or flat roof? That was the beginning of the Zehlendorf Roof War. And what's the situation today? We'll see…