In 1968 the West German World Fair Committee invited Stockhausen to collaborate on the German Pavilion at the 1970 World Fair in Osaka, Japan. Other collaborators on the project included the pavilion's architect, Fritz Bornemann, Fritz Winckel, director of the Electronic Music Studio at the Technical University of Berlin, and engineer Max Mengeringhausen. The pavilion theme was "gardens of music", in keeping with which Bornemann intended "planting" the exhibition halls beneath a broad lawn, with a connected auditorium "sprouting" above ground. Initially, Bornemann conceived this auditorium in the form of an amphitheatre, with a central orchestra podium and surrounding audience space. In the summer of 1968, Stockhausen met with Bornemann and persuaded him to change this conception to a spherical space with the audience in the center, surrounded by loudspeaker groups in seven rings at different "latitudes" around the interior walls of the sphere. In addition, Stockhausen would participate by presenting daily five-hour programs of his music. Stockhausen's works were performed for 5½ hours every day over a period of 183 days to a total audience of about a million listeners. "Expo" was written, as the title indicates, for these performances and was composed in Kürten in December 1969 and January 1970, at that time under the working title of "Trio". Between 14 March and 14 September 1970, "Expo" was played and sung many times at the German Pavilion at Expo '70, in daily performances by twenty different musicians including the composer. The English group Intermodulation (Roger Smalley, Tim Souster, Peter Britton, and Robin Thompson) performed it a number of times and made recordings for the radio.