|This article is about an older version of DF.|
Bridges allow dwarves, traders, and their cargo to travel over terrain that would normally be impassable. Bridges can be placed over rivers and other water (as well as the ice sheet in some freezing maps), swamp tiles, channels, magma, and the chasm. They can be made of raw stone, wood, metal bars, or blocks of any material. The magma flow can only be bridged by a steel or adamantine bridge. However, the bridge's overall material is determined by the topmost item in the list - thus, you can use a single steel bar and four brass bars to cross the magma river, provided you made the steel bar first.
Bridges built within the mountain can be attached to levers or pressure plates and made to retract or raise. These can be used either to deny passage to enemies, or to kill them: a drawbridge lowered on any creature will kill it instantly. Moats (built from channels/ponds) and "Trojan Horse" entrances spanned by a bridge are both very effective forms of fortress defense.
Types of bridges
When a bridge is placed outdoors, it is just an ordinary bridge, and cannot be assigned any special types. When built underground, however, a bridge can be either retracting or raising, like a drawbridge. Retracting bridges can be built without the need for an open area on the other side, while raisable bridges can crush anything they are lowered over, and will form a sturdy blockade against flying or aquatic assault while raised. In either case, the bridge must be linked up to some form of a trigger via mechanisms for it to move; normally, this would be either a lever or a pressure plate. When placing a bridge, press , , , or for a drawbridge in one of the four cardinal directions, or for a retracting bridge (the default). The direction that a bridge raises can be slightly confusing: If a bridge raises to the left, then it forms a wall on the left side when raised, and when lowered it will squash anything to the right.
Even if a bridge is raised or retracted, you can not place (uild) anything else in the space the bridge normally occupies. So a pressure plate to lower a bridge onto enemies can't be placed underneath the bridge area itself. You can build bridges over channels (for instance, to span a moat), but only after the channel has been filled with water from a river at least once and no longer registers as an actual building to the command. You cannot build a channel beneath a bridge after the bridge has been built.
Bridges as traps/weapons
Any creature (including dwarves) caught under a drawbridge when it lowers will be killed instantly. The creature will completely disappear, leaving neither a corpse nor any of its gear, giving it the nickname "Dwarven atom smasher". Creatures caught on top of a drawbridge when it raises will be sent flying through the air, much like a catapult stone. In the words of Toady One, "The relevant function in the code is called flingify."
Note that bridges built outside the mountain cannot be linked to levers to be used as goblin smashers.
When building a bridge, you can select a number of pieces of material. Each piece of material increases the number of squares the bridge can occupy, up to a limit of 10 squares in width or height.
For raw stone, stone or glass blocks, and wooden logs:
- Size of Bridge = (Material Amount) x 4 - 1
- Size of Bridge = (Material Amount) x 2 - 1
When sized and placed, the dwarves will only use the minimum amount of material needed. For example, if you want a 5x2 bridge, and select four stone blocks to build it with, the dwarves will only use three of the blocks.
Bridges can mix material types (stone, metal, wood, etc.) and gain no benefits from using only one type of material, but the color (and material for game terms) is determined by the topmost selected material from the material selection list.
Bridge construction may generate a path-finding error if a dwarf attempts to use a chosen piece of stone that is inaccessible. To work around this you can use a different kind of rock.
Another common cause of path-finding errors is attempting to build a bridge in such a way that it would cover inaccessible loose rock or other materials that the architect would need to move out of the way. This often happens when a temporary bridge is built across the river or chasm, space is mined for the "real" bridge, and the temporary bridge is then removed. To solve this, leave the temporary bridge up until the main bridge has been fully designed by an architect.
Bridges, along with certain other buildings, may cause happy thoughts for dwarves that pass by them. Comments that your dwarves may have about your bridge can escalate from fine, to great, to completely sublime. The better the bridge, the happier your dwarves. Building a bridge using smoothed blocks, metal bars, or glass blocks increases the value of the bridge making it much more likely to evoke admiration, as will using a highly skilled building designer and mason (or carpenter or metalsmith, depending on the material).