A contrarian figure in the debate on French collective housing during the Trente Glorieuses, Émile Aillaud designed over 15,000 social housing units over several decades, never aligning himself with the technocratic logic imposed by the central government but rather bending it to his own sensibilities. One work in particular, the Cité des Courtillières, built in Pantin between the 1950s and 1960s, seems to distill the themes of his work, constantly balancing lively construction experimentation, the attempt to dissolve architecture into an already mature idea of the city-landscape, and an early attention to the psychology of the inhabitant. This project still lends itself to analysis today, revealing the compositional methods with which Aillaud constructs the ‘hidden order’ behind the apparent extravagance of architectural forms. Through the story of this work, this book also traces the contours of a much larger fresco, which coincides with a rapidly erased chapter of 20th-century residential architecture, whose lessons are yet to be learned.