Marathon began in 1908 as the construction headquarters and chief shipping terminal for Henry M. Flagler's Overseas Railway to Key West. Thousands of workmen and immense quantities of material and supplies passed through it. At nearby Knight's Key dock, trains from New York met steamers from Havana daily until the railroad reached Key West on January 22, 1912. West of town, the Seven Mile Bridge, resting on 546 concrete piers, was then the longest railroad bridge of concrete and steel in the world. A storm on September 2, 1935, ended railroad operations, and ten years later the Overseas Highway, built on the same track bed and bridges, began to be used.