A bridge which was used to provide access to a fortification, and when in the raised position it closed the entrance. Generally, a drawbridge was hinged at the bottom and free at the top, and could be drawn up to prevent and enemy gaining entry. The drawbridge usually spanned a ditch or moat, or the part of a ditch or moat between the fortification and a causeway. Its simplest form it consisted of a movable plank; others were pulled up by chains worked by pulleys or a windlass. A later development was the hinged platform; which could be raised by pulling up chains attached to the outer corners, these chains passed through slots above the entrance and were attached to a windlass in the chamber above the entrance. The most elaborate type worked on a counterpoise system; the chains were suspended from beams which, when the bridge was drawn up, fitted into recesses provided above the entrance. Another type worked on the pivot principle, where the inner part of the bridge was moved into a pit while the outer part rose to completely cover the entry, also known as a turning bridge (L. pontem torneicuim). See bascule bridge, hinged bridge.