Walking through Le Corbusier's exhibition at the Museum of Modern Art, I was surprised by how many of the great modernist architect's designs were never built. They were simply too radical, and none more so than his 1925 proposal to demolish two square miles of downtown Paris.

It's probably a good thing the architect, born Charles-Édouard Jeanneret-Gris, didn't get his hands on Paris. The area he would have destroyed, including the 3rd and 4th arrondissements on the right bank of the Seine, is today among the prettiest, hippest, and most architecturally significant neighborhoods in the city. What's more, the replacement of organic urban areas with huge new developments has been criticized since the 1960s for sapping the vitality of cities.

All of that said, let's take a moment to appreciate how cool Le Corbusier's Plan Voisin would have been.

To start, demolishing central Paris made a lot of sense in the 1920s. The formerly aristocratic Marais district had fallen into squalor, characterized by poor sanitation, disease, and overcrowding, as chronicled by Marybeth Shaw in "Promoting An Urban Vision: Le Corbusier and the Plan Voisin." By 1921 in the Beaubourg area, 250 out of 276 houses were marked uninhabitable due to tuberculosis contamination.

Le Corbusier wanted to replace this urban blight with something incredible.