40d:Trap design

This page is one of several inter-related articles on the broader topic of defending your fortress and your dwarves. This page will focus on the theory and design of complex traps, mechanical systems and other automation for defending your fortress, and also on unusual uses of simple mechanic's traps.

See the Defense guide for a general overview of threats and considerations for fortress defense.

For suggestions on training, organizing and deploying soldiers and militia, see Military design.

Many defenses rely on complex traps as a central component, that are, essentially, the defense themselves. For designs that could be adapted to use any complex trap, see Defense design.

For suggestions on disposing of nobles and other unwanted residents, see unfortunate accident.

For a basic overview of how the different machine parts work and work together, see machinery.

Editors & Contributors - Please see top of discussion page before posting.

Basic traps

These are the simple traps that are placed by a mechanic. They require one mechanism but do not require levers or triggers. They can be a "first defense" for a fledgling fortress, but they can also be combined into key parts of more complex set ups.

Note that, in combat situations, Mechanics (and others) have a nasty habit of wanting to clean or reload traps when they are triggered, regardless of who or what might be out there as well. Forbidding traps after they are built will keep Urist McGoblinBait from deciding to reload a stone trap in the middle of a siege. Just remember to unforbid them when things calm down, so the traps are all ready for next time. Or keep all traps unreachable with drawbridges or orders.

Simple traps will also be triggered if your own dwarves or pets fall unconscious on them.

Stone fall trap (b-T-s): This is the easiest trap to build, so you can easily build them in large numbers. Building lots of them is an easy way to earn experience for your mechanic, and add to the depth of your fort's defenses at the same time. Surround every intersection and stairway.

Cage trap (b-T-c): A very powerful type of trap. Maybe even too powerful - currently, even a wooden or glass cage can hold indefinitely any creature, even trolls and megabeasts. Also, a cage trap never fails. A large creature can shrug off damage from a stone or weapon trap, but nothing can escape from a cage. Use cage traps as your outermost traps to catch the occasional wandering animal, or angry wounded elephant or unicorn, or even zombies.; By connecting a trapped animal in a cage to a lever, you can remotely release that animal. (Note - not all wild beasts will attack goblins.)

Weapon trap (b-T-w): The gold standard of lethal traps. This is the only simple trap that works repeatedly without reloading. They do get jammed, however. View the trap with the items in room t mode, and if there's a corpse inside the trap, it's jammed. None of the weapons on a jammed trap will function. It may be wiser to have several weapon traps with fewer weapons, rather than a smaller number of ten-weapon traps.; Using crossbows in weapon traps avoids the problem of jamming, but they must be kept loaded with ammo. Mechanics will load them with any ammo that is not forbidden. Hammers seem to jam less than swords or axes, and spears seem to jam the most. Your dwarves will attempt to unjam traps unless otherwise forbidden.

Using simple traps

Scattered traps: One option for outside defenses is scattered traps. Most hostile forces will flee if they take enough casualties, and stone-fall traps can be quite damaging to goblins and are easy to set up. Cage traps work even on Bronze Colossi and Dragons. Make sure your dwarves working outside stay near your traps - a fisherdwarf who goes wandering screens away from the nearest trap is not protected.

Linked traps

Complex traps and automation rely on linking doors, hatches, floodgates, bridges and mechanic's traps to triggers such as a pressure plates or levers. They require at least three mechanisms, one for the trigger and two to create the link. The trigger can be located any distance from the trap, typically close for a pressure plate or far away for a lever. When the trigger is activated, it sends a signal to the linked device. That signal is not "toggle", but it's specifically either to "open" or to "close".

For a system that repeatedly activates automatically and regularly regardless of enemies, see Repeater.

Trap strategies

Bait animals: Enemies will hunt down and kill friendly tame animals wandering outside if they have nothing better to do. Put a puppy on a chain in some random spot outside, build a few columns around it to reduce the chance of them shooting it, and trap that area to hell and back. Also known as the "Tar Baby" strategy.

Obstacle Course: Combining some intentional cave-ins, lots of cage traps, some weapon and stone fall traps, channels, and pressure plates is a sure-fire way to fend off an invading goblin army.

Circular path trap: Channel around a 1-tile-wide path, leaving one support under it. Connect it to your base with a bridge so enemies will take it. Place a pressure plate at the end, linked to the support and another bridge into your fortress. Line this area with weapon traps and line the exits of the subterranean area underneath this with cage traps. The area underneath must also lead to your base so the enemies will walk into the cages. Then build another area just like this except have the entrance bridge be retracted/raised and have the first pressure plate link to it, so it is an endless game of cat and mouse.

Damage traps

These complex traps are designed to kill or maim.

Menacing spikes (b-T-S): Menacing spikes or upright spears can be activated remotely to pop out of the ground and impale anyone standing on that tile. Vast forests of these can make any area a killing field.; They will not jam. They are very deadly to everything including your dwarves and animals. Steel ones are fireproof.; Try planting a bunch of Upright Spear/Spikes in your main hallway, and link them all up to one lever. When invaders come near, give the order to pull the lever, but set it to Repeat. The lever will continuously be pulled and the spikes come up and down repeatedly, perforating most enemies in seconds. Note that this takes a lot of time and mechanisms to build.

Dropping the Hammer: Lowering drawbridges on invaders will crush them.; Try replacing the side wall of a part of your main entranceway with a drawbridge, big enough so it spans the whole hallway. To prevent enemies from wrecking it, you could dig a channel in front of it so its protected while its raised. Link the drawbridge up to a pressure plate or lever, whatever you prefer. Whenever you feel like it, activate the trap, and watch the drawbridge fall directly into the hall, utterly squashing anything beneath it. This can be done with minimal effort and used to smash invaders, unwanted immigrants, nobles, or simply to destroy your garbage. This is based on the Dwarven Atom Smasher.

Intentional Cave-in

Supports can be linked to triggers. Building a section of floor that is deliberately held up only by a trapped support allows for an intentional cave-in.

Invaders dropped into a pit can be wounded or killed. Or, in the case of a chasm, vanished entirely.
Dropping a rock floor on invaders will likewise do harm.
The cave-in will also knock nearby invaders unconscious. This will stun them, and also make them susceptible to simple traps (even if normally immune).

Water traps

These traps drown or wash targets away. Use with caution—carelessness can cause an entire fortress to be lost to flooding!

Level 0

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Level -1

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Level -2

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░ - Wall

+ - Floor

· - Open space

▲▼ - Ramps

X - Inflow

x - Outflow

-> - Direction of traffic

If enemies are in the middle of Level -1, open the inflow, then the water will first trap, and then drown them. If the pit is full, close the in- and open the outflow. You can automate this by using pressure plates, or if you want to have more fun, replace the water with magma (pressure plates and floodgates have to be magma-save then).

Magma traps

These traps incinerate targets, or possibly encase them in obsidian. Magma does not play favorites - read up (again) on magma, and use with extreme caution.

Sealed Fate: Create an airlock using two bridges or two doors. Make it a medium sized chamber, perhaps 10x10 or so. Channel out the floors around the rim, and rig up a system to pump magma into the room, or drop it from the roof. Enemies will quickly be destroyed, and with the magma in the channels, you can pump it out for future use or just leave it. The idea here is a re-useable magma trap; you can use this with a pressure plate, too. It also leaves behind any magma-proof items the invaders might have been carrying.

Magma Machicolation: One or more 1-3 tile refillable reservoirs of magma on the upper levels of a room, held behind magmaproof floodgates (or grates/bridges). When goblins gather under it, open the floodgates.

= | = | = | = | = | = | =
. | 1 |!g!| 2 |!g!| 1 | 1
. | 1 | 1 |!g!| 1 |!g!| .
. | . | 1 |!g!|!g!| . | .

Like with other designs, you need infinite magma (in the long run) and get only the magmaproof loot, but at least it needs much less magma.

If this design is built near ground-level grass, deadly bushfires may develop. This may limit its usefulness, but it could also deal further damage to your enemies, should they fail to recognize the dangers of fire and happily walk through it (likely).

Misty Surprise: A magma basin next to the path to your fortress, with some constructions held by supports over it, linked to a lever. To fire the trap, pull the lever, sit back, watch the constructions splash into the magma, and enjoy how the goblins ignite in the ensuing deadly magma mist (optional: laugh maniacally).; As usual you only get magmaproof loot. The effect is unfortunately somewhat random, but this design works well with a finite magma supply, as with a magma pool (if you really use only constructions).; The usual safety precautions concerning cave-ins, magma and magma mist apply.

Automation & misc trap designs

By clever and creative use of various elements, it is possible to create impressive automated systems that fill a variety of functions.

For a system that repeatedly activates automatically and regularly regardless of enemies, see Repeater.

See also computing for other, possibly related ideas.

Funnel trap: In any area you have observed animals to be common, create a large barrier in the shape of a cross - it can be a wall, a channel, slopes that have been removed, or a combination. Leave the very center tile of this cross open to traffic, and cover that central area with cage traps. If the wild creatures try to migrate across the map where you have constructed this, they run into the cross, and have a 50/50 chance to go around or through - if they go through, you've got them. The bigger the better.; It will also work against ambushes and sieges, with cage traps or lethal ones.

Chasm trap: The easiest chasm trap is just a retractable bridge, very high up or over a very deep hole; instead of flinging invaders when raised, it just drops them.; A more complicated collapsing spiral trap can take out ten goblins at a time.

          +++
..........+++
.++++++++#+++
.+╔══════.     # = retractable bridge 
.+║++++++.
.+║+╔══╗+.     + = floor
.+║+║A+║+.
.+║+╚═+║+.     . = open space
.+║++^+║+.
.+╚════╝+.     ^ = pressure plate
.++++++++.
..........     A = bait animal

The goblins are lured in by a restrained bait animal, and can't shoot it due to the surrounding walls. Just before they reach the bait, they trigger a pressure plate that retracts the bridge and collapses the support holding up the whole spiral. Goblins, bait animal, walls and all plummet into the chasm.

When building, you will need to build a span of floor underneath, for the support, as bridges do not support constructions (which is also why you want a bridge as the access, so it will not hold up the trap*). You will also need to have a floor tile between your floor and solid ground or wall while constructing, as the bridge alone will not work as a base, but you can remove it once the support is in place.

(* A set of floor bars or grate would work as well, but the bridge can aid in the (re-)construction of the trap.)

Land Mines: In any suitable open area which hasn't been dug out underneath, build a support and an adjacent multi-use pressure plate set to trigger on creatures (but not citizens), link them together, then build floor tiles above the support and pressure plate. When an enemy steps on the pressure plate, the game will pause and recenter the view with the announcement "A section of the cavern has collapsed!", at which point the enemy will be crushed and its companions will be stunned or knocked unconscious by the cloud of dust (and revealed, in the case of an ambush). As added bonuses, by using a multi-use pressure plate, the collapsing floor will deconstruct the plate and leave its mechanisms lying on the ground for reuse, along with all other building materials used (the materials used to construct the support and floor tiles, plus the mechanism used in the support) - alternatively, if a single-use pressure plate is used, both of its mechanisms (but not the one used in the support) will be destroyed, making this one way to dispose of low-quality mechanisms created by unskilled engineers (aside from selling them to caravans, dumping them in magma, or crushing them under a drawbridge).

Bridge Land Mines: Although this takes quite a few mechanisms and a lot of carpenters to pull off, you might be able to create a minefield on a bridge. Create a very long moat and a bridge crossing it. Make sure this bridge is not your outermost bridge. This bridge should be at least 20 squares long, but make sure it is no more than 4 squares wide. Then set up a ton of pressure plates in a checkered pattern, build a floor above the bridge, and make supports next to the pressure plates. Then remove the floor tiles not on the supports, destroy the up-stairs on to the floor, and link all your pressure plates to a support. As soon as a goblin walks on them, the floor caves in and makes an explosion knocking him and the friends he has near him off the bridge drowning them.; This should not be used as the only defense. Make sure you have other traps at the ready in case of large sieges.; NOTE: This is a very expensive creation and should only be used late in the game when you can spare lots of stone/wood/mechanisms. The bigger the bridge the more effective the trap.; Retract bridge 2 to force invaders to take the long way, first running along the wall (to the west in this diagram) and then zig-zagging back for maximum exposure to your ranged units on the walls above them. The pits at the base of the walls are necessary to target down one z-level at enemy units.; (Note - Traders will NOT stop at your fortress unless there is a clear, 3-wide path to a Trade Depot when they arrive. Bridge 2 should be kept down if you want/expect Traders.); Bridges 1 and 3 can be put down to allow enemies into this pit entrance, then retracted again to trap them in the kill zone. Note - Attackers must have a complete "path" to where they want to go, so bridge 3 must be down to lure them in.

Dragonfire Pillbox: NOTE: This trap has not been tested yet. Please verify if this will work or not.; First, capture a Dragon.; Then dig out or build a small bunker so it faces your main entrance. Leave a space so the Dragon can fit in it, and install his cage there; link this to a lever. Build five wall sections to surround him on the sides and behind him so he faces where you want him to. Dig three channels in front of him so he cant escape but he can breathe fire. Build 5 floodgates or doors adjacent to the channels and link everything up to levers. Optionally you can build some Fortifications adjacent to the floodgates to protect the Dragon from arrow fire.; When all is said and done, pull the lever and release the dragon. Naturally he would try to kill something but cant because hes surrounded by walls, and the channels stop him there too. Now you can open the floodgates during an attack and watch as the Dragon immolates invaders and immigrants alike. You can close the floodgates once the danger has passed to avoid him torching your own Dwarves.; Should you wish to recapture the Dragon, perhaps to move him elsewhere, you can channel out the back or side wall of the bunker and plant a small drawbridge there, kept raised most of the time. Plant a single Cage Trap past the bridge; you can lower it at any time to recapture the beast.; For less effort, fire imps work just as well, but also offer far less firepower.

Degrinchinator: Observe: http://mkv25.net/dfma/movie-231-degrinchinator

Twin Paths: Vexed by how to safely collect loot and clean traps when ambushes are always ready to spring? Don't want to sacrifice animals? This trap is like the above-mentioned chasm trap with one difference: When the bridges are retracted, anything on them falls into a pathway the same shape as the bridge pathway. This pathway contains many (or ideally is covered by) weapon traps. A lever attached to all the bridges can spring or reset this trap, and a pressure plate part of the way down the bridge path can catch ambushes. This method drops invaders or ambushers to where your dwarves can safely loot them, and if one of your own dwarves is caught, the weapon traps do not target them.

The Dwarven Mousetrap: a.k.a, Suicide Booth; It is well known that Thieves can cause plenty of problems in a fortress; They take your valuables, they disable your doors, they may even kill an animal or two on their way out. But what is not as well known is that Thieves also have a rather annoying tendency to pull levers they come across, or let animals out of cages ^[Verify]. This can go from a simple annoyance to a downright danger, but there is a way you can capitalize on this. You know what they say, "Curiosity killed the cat"...; Build a lever outside or close to your entrance, wherever you think is best, and nearly surround it with 7 wall sections, leaving it open on one side. Install a Menacing Spike in the one open spot, and link that to the lever. Pull the lever once to lower the spike; The trap is set. Now, the next time a thief decides to visit, he may just be distracted by that juicy lever and end up pulling it, resulting in the spike promptly raising up from the ground that he is standing on, impaling him on the spot. This trap has some utility, and can be used for easily disposing of unwanted Dwarves like Nobles by simply having them trip the lever. Should the spike fail to kill the creature, it will likely be severely wounded, and easy prey for your soldiers and/or war dogs.