This paper investigates the establishment of the ville nouvelle as a colonial archetype through which French planners performed historical conservation in Islamic cities. In their early twentieth-century schemes for restructuring colonial Arab cities, especially in North Africa, French planners often preserved the ancient Islamic city or medina and created a ville nouvelle, a modern city, adjacent to it. The new city boasted large boulevards, squares and gardens, buses and tramways, and conduits for water and electricity, whereas the old city was conserved in its entirety and was denied new infrastructural and technical amenities. Such conservation of ancient urban ensembles was not practiced in France at the time. There, the protection of landscapes and monuments had been the subject of laws whose application came only after massive destruction that demonstrated the necessity for conservation. In Arab cities, however, French planners took active measures for the protection of monuments before planning started. The paper shows how the notion of the historic city, as well as the binary opposition between it and the modern city, was established in the French colonies. I examine ville nouvelles designed by French urbanists Henri Prost and René Danger for cities in Morocco and Algeria: Rabat, Fez, Marrakech, Casablanca, and Oran. I show how these planners applied the nineteenth-century standards of preserving monuments that were developed in France to the entire historic city. In Prost’s and Danger’s colonial planning, the modern city and the historic city were based on radically different principles. Rather than building the modern city on top of the old one—as practiced by Georges-Eugène Haussmann in the French capital and generalized in Germany and Austria by Joseph Stübben—the modern city was displaced. It was supposed to develop outside the historic core and according to its own logic.