One Sunday afternoon in 1928, Raymond Poincaré, the Président du Conseil des Ministres (Prime Minister), returned from a weekend at his property at Sampigny in the Lorraine region. The weather was beautiful and the trip was going smoothly until he arrived at Chelles, on the eastern outskirts of Paris. There, he found himself behind a long line of cars. An automobile accident ahead had closed a portion of the highway and Poincaré, unable to move, encountered first-hand the realities of unregulated Parisian sprawl. From his car window, he witnessed, ‘une banlieue interminable, sans ossature, où le hasard seul semblait offrir un passage, [avec des] habitations noyées dans un indescriptible chaos’ (Remaury 146). The narrow streets and substandard construction, reminiscent of pre-Haussmann Paris, seemed to startle him. Once back in the city, moved by what he saw, Poincaré suggested a formal region-wide planning authority to normalize not only suburban housing construction, but also the increasingly over-burdened road network outside Paris's city limits.

Six years later, on 14 May 1934, French urbanist Henri Prost presented Albert Sarraut, Minister of the Interior, with his ‘grand album contenant le projet d'aménagement de la région parisienne (Plan Prost),’ a dossier with his detailed plan for Paris's future (Remaury 152).