Louis Henry Sullivan headed the so-called Chicago school of architecture, which was distinct by its development of functional design along with modern materials. Sullivan's follower Frank Lloyd Wright absorbed from his 'lieber Master' (dear master) the German romantic tradition of organic architecture. He developed a new and original approach to residential design before World War I, which became known as the "prairie style." It combined open planning principles with horizontal emphasis, asymmetrical facade elevations, and broad, sheltering roofs. Robie House in Chicago (1909) and the Guggenheim Museum in New York City (1946–59) are two of his seminal works.