This paper explores the fierce debate between engineers and urban planners over the validity of disciplinary tools at the time of the construction of the Interstate Highway System in the United States, particularly those moments when the system invaded the heart of the existing city. This debate, far from a collegial discussion over the future of the city, was a collision between viscerally held positions. On the one hand, engineers, strongly linked to prevailing political–economical structures, redefined the city through the pragmatism of a method. On the other, architects and urbanists argued for a project that would define a theory of “the urban,” or recover a notion of urbanity. In this context, method and theory seemed irreconcilable opposites, the former associated with notions of efficiency and seen as an authority able to respond to the project at hand, the latter understood to be an overly specific instrument, unsuitable for the largest public works project in American history. Three conferences, Hartford (1957), Sagamore (1958) and Hershey (1962) became the stage for a disciplinary debate between architects and engineers in the search for professional validation.