Walk around any famous city and layers of history start to emerge. In London, Roman walls are dwarfed by office blocks. In Rome, ancient treasures like the Colosseum stand shoulder to shoulder with buildings from the Renaissance. In New York, skyscrapers from the 1920s and 1930s predate enormous glass towers.

Rome, Italy --Istanbul, Turkey -- Paris, France -- Beijing, China -- London, U.K. -- New York City, U.S.A.