Drawbridge
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A drawbridge is a type of movable bridge typically associated with the entrance of a castle, but the term is also used to describe modern bascule bridges and lift bridges.
The most common type of drawbridge consists of a wooden platform with one fixed side (normally with a hinge), and the other side attached to the wall it is raised against by rope or chains. Pulling on the chain raises the bridge. These chains were usually operated from a floor higher than the drawbridge.
In the Middle Ages drawbridges where often used to allow or deny access across a moat or ditch. They could be let down to allow people across, or pulled up to deny entry into the castle.
Now, with cars and trains in need of crossing small waterways without blocking boats from passing, drawbridges have a more peaceful reason for their existence.
In Queensland, diamond crossings between narrow gauge cane tramways and main lines are being replaced by drawbridges, so that the rails of the main line are completely unbroken by gaps or weak spots. This also allows the main line speeds to be raised.