Of all the art forms none is as immodest as architecture. It thrusts itself in the eye of the viewer, caring naught for opinion. The Ozymandian statement is simple: ‘Here I am. Gaze upon me.’ Given the egos of many architects and their clients, the potential for visual horror on a gargantuan scale is terrifying. Indeed, when you think about it, it is quite remarkable that our cities look as presentable as they do. Even more remarkable, though, is what they could have looked like if no holds had been barred. Fancy a Parisian chateau in the shape of an elephant? A dome to cover part of Manhattan? A London cemetery in the shape of a pyramid? As Philip Wilkinson explains in his excellent Phantom Architecture, all these projects were once on the cards.

With the benefit of hindsight, some architects nailed things on the head. In 1490 or thereabouts, Leonardo da Vinci outlined a plan for a multi-layered city that would provide clean air to prevent the spread of disease and an underground drainage system to banish sewers beneath the streets. There