In the midst of the Arizona desert in the US stands a half-built town that has attracted architects from around the world for the past 35 years. Arcosanti is an experiment in ecological city design. There are no cars since the space is planned for pedestrians, and there are large, compact living structures built next to huge solar-heated greenhouses where the residents' food is grown. Electricity comes from wind and solar plants, and the water from the nearby river is carefully husbanded. Only 60 to 100 people live there now, well below the 5,000 that Paolo Soleri, the architect who founded Arcosanti, envisions. But since the project launched in 1970, 6,000 architectural students have come to help with the building and learn about its design, and the site attracts 50,000 visitors every year.