The first suspension bridge with a horizontal truss-braced deck is credited to James Finley, who in 1801 built a 69 foot span across Jacob's Creek in Pennsylvania.  Suspension bridges become more economical to build than other types of bridges for spans greater than 1500 feet. Suspension bridges utilize cables that are attached to anchorages at either end, and draped over towers, to hold up the deck over which the traffic flows.  One of the most difficult and dangerous aspects of building a suspension bridge is the laying of caissons or cofferdams, used in constructing the foundations.  Cofferdams are built in place, whereas caissons are generally constructed elsewhere and moved into place.  They are used to support the towers.  John Roebling, one of the principal bridge builders of the late nineteenth and early twentieth century, became the premier builder of wire suspension bridges in the United States.  Renaissance philosopher-scientist Faustus Verantius (1551-1617) described three suspension bridge designs in his book Machinae Novae (c. 1615). 
    
     The George Washington Bridge (left) was built between 1927 and 1931, connecting Fort Lee, New Jersey to Manhattan.  It has two decks for vehicular traffic and a main span of 3500 feet; its total length, anchor to anchor, is 4,760 feet.  Its engineer, Othmar Ammann, originally intended the towers to be granite.  Because of cost considerations, he agreed to have a steel skeleton covered in concrete; the concrete was abandoned as well and the trademark steel frame construction was left as it was.  Ammann was quoted in Gay Talese's book The Bridge (about the Verrazano-Narrows) to say of the GW: "It is as if you have a beautiful daughter and you are her father."   







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