Giedion, Sigfried (zēkhˈfrēd gēˈdēôn) [key], 1883–1968, Swiss historian of architecture. Giedion was a student of Heinrich Wölfflin and close associate of Walter Gropius. He was a key figure of the International Congress of Modern Architecture (see CIAM) from its inception (1928), and taught at Massachusetts Institute of Technology and Harvard, where he became chairman of the graduate school of design. Giedion presented lectures at Harvard in which he broke with the German materialist tradition of 19th-century art history and described history in terms of constancy and change. These lectures were collected in Space, Time, and Architecture (1941). Among Giedion's other works are Mechanization Takes Command (1948) and the two volumes of lectures entitled The Eternal Present (1964).