Over a number of games, I've never had anything worse than goblins attack the surface entrance to my fort. These are easily dealt with by a few doors and long lines of traps. I almost feel sorry for them.

However, I have had rather more...Fun creatures attack from below - specifically Forgotten Beasts from the caverns. Since these guys are building destroyers, my measly stone doors barely slowed them down.

How can I build a defense that will keep monsters this powerful at bay, or better yet, destroy (capture?) them outright? Are there different tactics available at a cavern entrance vs. a surface entrance?

I prefer constructed defenses over armies, but I realize that for some beasties, the only answer may be a platoon of well-equipped veterans.

  • Have you tried murder holes + ballista?
    – tzenes
    Sep 2, 2010 at 16:15

2 Answers 2


A raised drawbridge or retracted bridge over a moat will stop all uninvited guests that can't fly. As you have noticed they are building destroyers so the drawbridge can be destroyed by a Forgotten Beast and it is no better than a retracted bridge to stop flying FBs.

A retracting bridge has the advantage of allowing you to make a manual trap if you time the closing of the bridge properly. I suggest you use a long bridge that leads to a long fall on spikes traps. As soon as you get the message about the uninvited guest, send one of your dwarf in the room where the lever to access the bridge is located (lock him there). It takes some time for the bridge to retract: you will need some testing to determine the optimal time to pull the lever (use pause then . to advance the game slowly). Long bridges are advised to let your dwarf some time to pull the lever -- dwarven stupidity should never be underestimated.

FBs don't activate traps but the spikes in the bottom of the pit don't need activation: they are always on. I'm not sure about the optimal fall distance but a fall of 10 z-level on steel spikes made short work of my last uninvited guest.

Flying FBs are another matter I suppose. I haven't played long enough to get flying Forgotten Beasts but I'm sure they exist and you will have to either wall the cavern entrance (b C constructions can not be demolished by invaders) or confront them with your army.

  • 1
    I highly disagree with "Retracting the bridge should be immediate". In my experience it takes some number of ticks to get a gate closed.
    – C. Ross
    Sep 2, 2010 at 17:05
  • @C. Ross: you're right, I've updated my answer.
    – BackStaB
    Sep 3, 2010 at 8:02
  • 1
    FYI: Falling on spike traps does no more damage than falling on bare stone. You can, however, set them to lever-active and have the lever on a repeating pull order, causing them to get stabbed at fantastic rates.
    – Daenyth
    Sep 3, 2010 at 18:27
  • A retractable bridge over a hole will stop even a flying forgotten beast. There's a pathfinding bug that prevents buildingdestroyer behavior from working if the monster can't find a way to stand next to the building. (For the same reason, a door at the top of a small hill is also indestructible.)
    – Brilliand
    May 9, 2014 at 23:03

Walls. Nothing can destroy walls.

(Well, except for cave-ins, that is. And dwarves, of course, if ordered to do so.)

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .