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.

A bridge defaults to a single tile in size. You'll need to change the size to suit your needs; the bridge's dimensions can be set anywhere up to a square 10 tile on a side. A bridge will require both architecture and masonry (or carpentry or metalsmithing if wood or metal is used) to complete. The material required for a bridge is less than the material required for building an equivalent area of floor tiles, and when a bridge is deconstructed the materials are deposited on the ground next to where the bridge stood rather than falling down into the open space it spanned.

Unlike raising bridges, which require an area of solid ground, retractable bridges can be built using existing bridges as their sole means of support.

If the only path to your trade depot is over a bridge, the depot will be inaccessible to merchant caravans, even when down. A potential workaround^[Verify] is to offer a second path which you can block off using things such as lever-operated doors. This path can be easily walled off to protect against such things as trolls.

Drawbridges and retracting bridges

A bridge can be connected to a lever or pressure plate 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. That's why drawbridge is called the dwarven atom-smasher. 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.

The delay between the time a lever is pulled and the time a connected bridge changes state is 100 steps.