A bridge of which either the whole or a part is made to be raised up, let down, or drawn or turned aside, to admit or hinder communication at pleasure, as before the gate of a town or castle, or over a navigable river or canal.

A bridge over a moat or ditch that can be drawn back or raised from the inner side.

a large heavy door that lowers across a moat to enter a castle, and raises to block entrance

The moveable section of a wooden bridge or causeway, often over a moat, operated by counterweights to keep an enemy force from the easy approach to the gatehouse.