Of all the projects designed by Guy Rottier, Ecopolis “City without pollution” still manages to fascinate the contemporary observer. This proposal for a new ecological city is a surprising synthesis of the host of questions raised in architectural and urban thinking throughout the twentieth century. A legacy of modern urban thought closely tied to certain utopias, Ecopolis is also a successful anticipation of the issues raised at the beginning of a third millennium in which the majority of the world’s population is urbanised. Suspended between these two time frames, it offers a poetically technical illustration, at once utopian and concrete, of urban questions spanning the entire century and at whose centre is our relationship with nature in general and the sun in particular.