Part of the "Megastructures: The Visual Encyclopedia" book project, on sale now at http://www.neilblevins.com/megastructures/megastructures.htm
A Movable City would be a livable structure that could be moved, or would be in constant motion.
One of the originators of the idea was architect Ron Herron (in 1964-66). His Movable City, which he called a “Walking City,” had a beetle-type form. It was a city mounted on giant, telescopic steel legs. Other designs include hundreds of crawling legs (like a centipede), a city atop enormous treads (like the NASA launch pad crawler), or a city being pulled or pushed by large, motorized vehicles (like tugboats pushing a barge.) Due to their size, Movable Cities would travel at incredibly slow speeds.
Moving your city could have a number of advantages, such as avoiding natural disasters, escaping man-made disasters like irradiated zones caused by nuclear warfare, migrating to more temperate climates during winter months, or moving to new locations that had resources your city needed (once you’d used up those resources in your current location).