Work on Arcosanti, an experimental town in the Arizona desert, began in 1970. Architect Paolo Soleri wanted to build the city of the future: an innovative, eco-friendly single structure that would be self-sustaining and self-contained.

He saw it serving as a laboratory for ideas about ecology and urban architecture. And in some ways it has, incorporating sustainable practices that include blending the structure in with the landscape and orienting most buildings southward to capture the sun’s light and heat -- the roofs are designed to admit the maximum amount of sunlight in the winter and a minimal amount during the summer.

But 47 years later, Soleri’s vision remains uncompleted.

In fact, there has been no new construction at Arcosanti in more than 15 years. That’s partly the fault of new building codes -- the local fire company has put a halt to any additions until the dirt road that leads from the nearby interstate is paved. Originally intended to house a population of 5,000, only about 100 people live there now -- mostly volunteers and students studying architecture and the environment.