Whether we like it or not, that's the promise of supertall skyscrapers. In 2017, Kingdom Tower in Jeddah, Saudi Arabia, designed by Adrian Smith, will open at an estimated 3,280 feet, replacing the Burj Khalifa as the world's tallest building. Sitting inside the café at Rockefeller Center with Baker, I asked him whether the Kingdom Tower, at well over a half-mile high, might represent the outer limits of what man could design. Could he do, say, a mile? He thought about it for a moment. "Sure," he said. All he needed was the right client.