megalopolis

A "large city" named Megalopolis was founded in Greece in 371 B.C. to help defend the region called Arcadia against the city-state of Sparta. Though a stadium seating 20,000 was built there, indicating the city's impressive size for its time, Megalopolis today has only about 5,000 people. Social scientists now identify 10 megalopolises in the U.S., each with more than 10 million people. The one on the eastern seaboard that stretches from Boston to Washington, D.C., where the densely populated cities seem to flow into each other all along the coast, is now home to over 50 million people. But it's easily surpassed by the Japanese megalopolis that includes Tokyo, with more than 80 million inhabitants.