Quiz: Remember the definition of mal de mer?
either a drawbridge, a vertical-lift bridge, a transporter bridge, or a swing (pivot) bridge. The drawbridge, or bascule, is the best known; it may be single- or double-leafed. It originated in medieval Europe, probably Normandy, as a defensive feature of castles and towns. It was operated by a counterweight and winch. The drawbridge that formed one span of Old London Bridge was occasionally raised to permit passage of a ship having masts too tall to pass under at this point. In the late 19th century drawbridges began to be built specifically to aid navigation; the Tower Bridge, London, and the Van Buren Street Bridge, Chicago, were built almost simultaneously. Both were double-leaf bascules, and their success led to wide imitation; more than 20 were built to span the Chicago River alone.