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.

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Introduction

Complex traps and automation rely on linking doors, hatches, floodgates, bridges and mechanic's traps to levers or pressure plates. 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". By manipulating what does what and when, impressive results can be achieved.

To fully understand how these component objects work individually (before combining them into diabolical and complex combinations), see those articles.

Mechanic's traps

These use the simple traps that are placed by a mechanic, either individually or linked to 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.

Stone fall trap

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 your fort's defenses at the same time. Surround every intersection and stairway.

The only drawback is that if a wounded dwarf falls unconscious on a trap, it will be triggered, doing even more damage.

Cage trap

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. A wounded elephant or unicorn in your front courtyard is not good at all.

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

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. Hammers seem to jam less than swords or axes, and spears seem to jam the most.

Menacing Spike

Menacing spikes 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 can also be placed at the bottom of short drops to make the fall more deadly. Other, more subtle uses are also possible.

Dropping the Hammer

Replace 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' device mentioned elsewhere in the wiki.

Forest of Spears

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 pull off.

Tar Baby

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.

Obstacle Course

Combined with some intentional cave-ins, lots of cage traps, some weapon and stone fall traps, combined with channels and pressure plates can be sure-fire way to fend off an invading goblin army.

Create a small area 1 tile wide prefferably, and channel it out leaving one support under it. This MUST be connected to your base by a bridge so enemies will take it. the 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 at and mouse (sort of)

=Scattered traps

Another options 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. You just have to make sure your dwarves working outside actually stay near your traps - a fisherdwarf who goes wandering screens away from the nearest trap is not protected. A wall of traps is a passive threat to injure, kill or capture enemies who will happily walk right over them.

Damage traps

These complex traps are designed to kill or maim.

Water traps

These traps drown or wash targets away. Carelessness can cause an entire fortress to flood and be lost. Use with caution.

a water trap

Level 0

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Level -1

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Level -2

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• = - Wall
• . - Floor
• _ - open Space
• \ - ramp (direction should be clear)
• X - Inflow
• x - Outflow

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.

Automation & misc trap designs

Bridge Land Mines

Although this takes quite a few mechanisms and a lot of carpenters to pull of, 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.