This article analyzes the formative role of medieval theology and aesthetics in the development of postwar American architecture by focusing on the architectural theory and practice of Mies van der Rohe and Jean Labatut, both of whom became actively interested in Neo-Thomism from the late 1940s. More specifically, a closer look at their reliance on the work of Jacques Maritain, the preeminent promotor of Neo-Thomism, sheds light on the transmission and circulation of old and new concepts within twentieth-century architectural theory. (...) By revealing how Maritain’s ideas helped to codify the latter and thus exposed the premodern ideas at the heart of modern architecture, I argue that modernist aesthetics should be re-evaluated with regards to its definition of “the new” and its emphasis on the breakdown or mutation of premodern frames of reference. (shrink)