This event is not a built structure but an idea: Tony Garnier's thoroughly theoretical city design, published as "Une Cité Industrielle" (An Industrial City). Exhibited in 1904 and printed as a book in 1917, the drawings set out every part of an imaginary industrial city of 35,000 — housing, factory, hospital, station, school — according to a single architectural principle.

That principle is reinforced concrete. Garnier rejects the ornamented mass of traditional stone and brick and adopts the then-new iron-reinforced concrete as the basic material of the city's whole fabric. The buildings in the drawings are plain, geometric, flat-roofed, and unornamented; cantilevered slabs, slender columns, and wide openings display the freedom that reinforced concrete allows. This is, before Le Corbusier and the Bauhaus, an attitude that foretells the material and aesthetic of modern architecture.

Garnier's real contribution is at the city scale. He divides the city into zones by function (housing, industry, health, administration), separates them with green corridors, and sets up a circulation that prioritises the pedestrian — laying out the founding principles of 20th-century modernist urban planning (zoning, functional separation). The Cité Industrielle is thus the manifesto not of a building but of how reinforced concrete could shape an entire city; an unbuilt design that deeply influenced the built environment of the century that followed.