Pierre Patte’s view of an idealised Parisian street, a sectional illustration in his treatise Mémoires sur les objects le plus importans de l’architecture of 1769, occupies a pivotal position in the historiography and visual representation of crowds and crowded spaces, though not a single person inhabits Patte’s imagined space. Pared down and evacuated of human presence, Patte’s section provides a visual matrix for civic order that will be invoked and elaborated upon by both architects and artists in the ensuing century. This paper argues that, in both its form and dissemination, Patte’s idealised section sets the stage for more animated visions of crowded spaces filled with the dispossessed, the diseased, and the dying in the nineteenth century. We position Patte’s illustration between successive Enlightenment rationalist and biologically attuned views of urban space and public life, calling on the histories of philosophy, science, and the visual arts. Our approach highlights an ideational and operative space in which crowds come to demonstrate a hybrid character as both political and organic entities, each with their own histories and attendant risks. The accompanying tension between the ordered, rational space of the city and the risk of spontaneous contamination by crowds shadows the massive urban renovation of Paris under Haussmann. Visual responses to Haussmann’s civic refashioning by artists such as Honoré Daumier reveal the infectious power of crowds, reaffirming a modern tension between urban control and unpredictable, often unruly, populations. In their attention to order, both Haussmann and Patte approach the city as a body to be cared for, and this paper considers how Patte’s Profil d’une rue anticipates later debates about architecture’s capacity to both shape and control the urban “contagion” of crowds.