When it opened in 1964, the Verrazano-Narrows Bridge was the world's longest suspension span. The ends of the bridge are at historic Fort Hamilton in Brooklyn and Fort Wadsworth in Staten Island, both of which guarded New York Harbor at the Narrows for over a century. The bridge was named after Giovanni da Verrazano, who, in 1524, was the first European explorer to sail into New York Harbor. Its monumental 693 foot high towers are 1 5/8 inches farther apart at their tops than at their bases because the 4,260 foot distance between them made it necessary to compensate for the earth's curvature. Each tower weighs 27,000 tons and is held together with three million rivets and one million bolts. Seasonal contractions and expansions of the steel cables cause the double-decked roadway to be 12 feet lower in the summer than in the winter. (Source: NY Metropolitan Transit Authority)