‘After the Expo, everything was modern,’ still is a lasting catchphrase in the popular history of Expo 1958 Brussels in Belgium. Architecture, however, had already turned modern long before 1958. It might sound odd today, but the organisers of the World Expo had announced the Expo’s architecture as ‘not so much modern, but twenty years ahead of its time.’ Moreover, while progressivist architecture journals, both Belgian and foreign, expressed their general appreciation for the overall rapprochement they observed between modern architecture and the public, they also did not hide their disappointment on the average state of architecture at the Expo. The Belgian CIAM delegation even declared that the architecture of Expo 1958 was “a great fiasco.” How can this Expo then be considered a laboratory for architectural and engineering experiment?