Postmodern architecture emerged in the late 20th century as a rejection of the rigid formalism and functionalism of Modernism. It is characterized by three main things: the return of ornament and reference to historical styles; a mixing of styles and forms rather than pure aesthetics; and a preference for complexity and contradiction over obvious unity. Key Postmodern architects like Robert Venturi, Philip Johnson, Charles Moore, and Michael Graves experimented with symbolic ornament, historical references, and unexpected juxtapositions of forms. Their buildings conveyed meaning through signs and allusions to other times and philosophies. Later architects like Frank Gehry took Postmodernism in new directions through experimental deconstructed forms and unusual materials like metal alloys.