Erich Mendelsohn's interwar architecture engaged only briefly with the Expressionism of his work from the war years, most obviously in the Einstein Tower, and slightly less so at the Hermann Hat Factory in Luckenwalde, and the Weichmann store in Gleiwitz. Despite his antipathy towards paper, Mendelsohn did have a solo exhibition at the progressive Paul Cassirer Gallery in Berlin, in spring 1919. "Architecture in Steel and Reinforced Concrete" featured his wartime drawings. Beginning in 1919, Mendelsohn explored the horizontal dimension as an organizing element in architecture through a series of sketch studies for skyscrapers, an iconic modern building type. These drawings show towers made of many stacked layers, some with rounded edges, others with orthogonal forms, all emphasizing the horizontal direction. In 1926, Mendelsohn published his famous book America: An Architect's Picture Book, a revealing collection of images and text that bear witness to his interest in urban, architectural, and aesthetic modernity, as well as commercial and industrial culture.