This article investigates the role of Expo 58, the first post-war world's fair, in the development of contemporary planning strategies for administrative and cultural complexes in Brussels. It argues that the Belgian government used this Mega Event as a catalyst for the construction of high-prestige buildings situated in a central zone within the capital. It examines the early planning initiatives of the government-commissioned Cite administrative and its connections with Expo 58, thereby highlighting the engagement of the Belgian Welfare State with modern architecture in the planning of prestige projects. This article thus argues for an understanding of the great event and the Cite administrative as part of the post-war government's 'Exhibitionary Complex', and using the case of Brussels suggests ways in which the impact of Mega Events could extend beyond their material remains.