This article examines the development of the Lisbon metropolis in the period between 1940 and 1966, looking for the ways in which urban and metropolitan planning established design and organizational connections with infrastructural development. Two arguments emphasize the changing role of infrastructure—starting as the driving force of a national policy of public works committed to the political construction of a modern capital and becoming the unfulfilled backbone of a late industrialization policy associated with morphological disruption in the context of a fast growing metropolis. A third argument of synthesis claims metropolitan public space as a key to acknowledge and design interfacing spaces of infrastructural mediation.