Le Corbusier's Unité d'Habitation is the manifesto of turning an apartment block from a building into a vertical city — a community living in a single block. Its answer to the post-war housing crisis is not mass but system.

The block rises off the ground on massive reinforced-concrete legs (pilotis); the ground floor is thus emptied and left to public space and circulation — the building does not occupy the land but floats above it. The 337 flats interlock as two-storey (duplex) units that mesh in section; each flat opens onto both faces of the block and has its own balcony. Thanks to this interlocking section, an 'internal street' (corridor) is needed only every three floors — an economy of space. A shopping floor is set in the middle of the block, and on its roof a public terrace of a nursery, running track, and pool: the city is embedded into and onto the building.

The building's aesthetic comes from displaying its bare, formwork-marked concrete — béton brut — as it is; the 'brutalist' movement takes its name from this. Le Corbusier also sets all dimensions by his own measuring system based on the human body and the golden ratio (the Modulor) — architecture rests on a mathematics tied to human scale. The Unité is both the most influential and the most contested prototype of modern mass housing; it is the source, for better and worse, of the social-housing blocks of the following decades.