By the mid-nineteenth century Paris held a population approaching a million inside a medieval fabric: narrow streets, open sewers, cholera epidemics in 1832 and 1849. The task given to Georges-Eugène Haussmann, appointed prefect of the Seine by Napoleon III, was to open that fabric up.

The method was surgical. Straight boulevards were cut through the city; more than twenty thousand buildings were demolished for them and tens of thousands of people displaced. A single façade regulation was imposed on buildings fronting the new boulevards — storey heights, balcony lines, roof pitch and stone colour were fixed, and the uniform appearance of Paris today is the result. The invisible part mattered more: over six hundred kilometres of sewers, pressurised water mains, gas lighting and four large parks. Cholera never returned at the same scale.

The project was sharply criticised at the time as well. The demolitions pushed working-class quarters out of the centre and rents rose; that wide boulevards made barricades harder and the movement of artillery and cavalry easier was an aim discussed openly after the risings of 1848. Haussmann was dismissed in 1870 amid arguments over financial irregularity, but the model remained: from Barcelona's Eixample to the late-nineteenth-century regulations of Istanbul, from Buenos Aires to Cairo, the scheme of boulevard, uniform façade and infrastructure spread through the cities of the world. Both the technique of modern planning and its basic question — whose city is transformed, at whose cost — were established on this site.