A bridge thrown over a ditch or ravine, which may be drawn up or let down at pleasure, one of its ends serving as an axis or joint for that purpose, while the other is connected by means of chains to two strong levers, called plyers, which are framed together with other timbers in the form of a cross, and are supported by two jambs, on which they swing. Bridges of this kind are most common in fortresses, to cut off communication with the surrounding country. In canal navigation, and in wet docks, swing bridges that turn horizontally upon one end as an axis have almost wholly superseded drawbridges.