Even before the Unitedstatesean President Truman urged the attendants of the 1945 United Nations Conference on International Organization to see themselves as “architects of the better world,” the field of global governance has proven to be a fertile ground for metaphors drawn from architecture. Indeed, in the collective imagination of practitioners and scholars alike, the international legal order appears as a vast and towering edifice: a veritable “architecture” that overlooks “areas” of governance sustained by figurative and normative “pillars.” But international law’s castles, of course, were not built solely in the air. For the metaphorical use of architectonical language only hides international law’s profound lack of engagement with the material and concrete spaces in which the “international” is produced, contested, and disputed. Conversely, in this dissertation, I take the “architecture of international cooperation” as a relevant question for international legal history. Instead of taking purpose-built environments for granted, I trace the birth of what I call the “international parliamentary complex” during international law’s “move to institutions” in the short twentieth century, (1919-1998). With this, I make reference to the emergence of buildings that claimed to serve as “international parliaments” throughout this period —especially those linked to universal or regional International Organizations. I trace this arc of emergence from “interwar” Geneva to the end of the Cold War, highlighting how this tendency to “parlamentarize” international relations mutated throughout the century.