A drawbridge is a type of movable bridge typically associated with the entrance of a castle. The term is often used to describe all different types of movable bridges, like bascule bridges and lift bridges.
In the Middle Ages, drawbridges were 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.
Another rail use of drawbridges was on the Listowel and Ballybunion railway in Ireland. This was a sort of monorail, where trains hung on either side of a fence-like track. Road crossings were either a gate-like Stuart section of track or twin drawbridges, that allowed crossing at rail level.