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 (1 + area/4, rounded down), 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. However, the same cannot be said of other structures such as floors. The game will allow the structure to be placed, but as soon as it is built, a cave-in occurs and the unfortunate dwarf constructing it falls to his death (bug 000436).

Drawbridges and retracting bridges

A bridge can be connected to a lever or pressure plate to become a drawbridge or trapdoor. When the lever is pulled, they will raise or retract in the 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.

A drawbridge, when raised or lowered, will crush anything standing on the tile that becomes a wall and anything that is standing where the drawbridge exists when lowered, respectively. This has earned it the name dwarven atom-smasher. Some players may consider the crushing power of the drawbridge to be an exploit — the only units that survive the smash are megabeasts, demons, and the ultra-fearsome wagon. These creatures will also prevent a retracting drawbridge from operating while they stand on it.

Anything standing on a drawbridge when it raises will be flung anywhere from zero to one Z levels upward and up to 10 units in any other direction. This applies to all items and units^[Verify], including flying creatures who happen to be on the same tile as part of the bridge at the time. The creatures will usually come out unconscious from the fling, and flying creatures may drop out of the sky.^[Verify] (To see what happens during a fling, view the Stone Fling DFMA movie.)

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.

If a bridge is built outside over a channel, anything under the bridge counts as inside for the purpose of preventing cave adaptation (but not for the "stay inside" order).

Interestingly, building a bridge over a constructed floor will allow dwarves to deconstruct the floor through the bridge without disrupting the path across said floor (especially if the floor is being used to bridge an area). Conveniently, the materials used to construct the floor will be left on top of the bridge, rather than being dropped down below it.