40d:Bridge

A bridge is a building (not a construction) that spans multiple tiles allowing dwarves to go across water, magma, and other obstructions. Bridges are built from the build menu, under bridge. The delay between the time the lever is pulled and the time the bridge changes state is 100 steps.

Drawbridges and retracting bridges

A bridge can be connected to a lever to become a drawbridge or retracting bridge. When the lever is pulled, they will raise or retract in a direction specified at construction. The direction that a bridge raises can be slightly confusing: if a drawbridge raises to the left, then it forms a wall on the left side when raised. A drawbridge that raises requires a floor underneath the side towards which it will raise (on the tiles where the "wall" will form when raised); remember to take this into account when digging.

Anything under a drawbridge when it is lowered will be utterly killed/destroyed, including all equipment. Any objects or creatures on a drawbridge when it is raised will be flung several tiles and stunned or injured. Some players may consider the crushing ability of a drawbridge to be an exploit if deliberately used.

A retracting bridge is less vicious; when retracted, any object or creature on the bridge will plummet if there is a pit beneath. When extended, the bridge causes no harm to anyone in its path.