The pit trap has now been properly tested. Two sieges of goblins (about 2 pages total in each siege) and a siege of armored undead were all broken.
To better deal with giants, ettins, and other large invaters too big to be dropped, they're simply caged, drowned, then dropped into the pit to be reanimated by the evil biome. This has been the general approach for all caged creatures. Live giants tend to kill too many zombies before dying, and then reanimate in a damaged condition, which is not ideal.
There of course is a lot of potential for improving the design:
- One of the biggest weaknesses is when goblins are dropped into the pit, they occasionally dodge out of it through the wall and into the ballista arrow collection zone.
- Falling items and corpse pieces sometimes fall through the floor to the z-level below if it is mined out. All the ballista arrows that clear the whole length of the range end up falling into the catacombs because of this.
- The marksdwarf bunker should have a gap to prevent goblin archers from so easily shooting in at the dwarves.
- The lever room could be closer to where dwarves typically idle. Probably a good idea for all levers in general really.
- More space around the exit to give the melee dwarves some room to assemble without being split across walls would improve the mopping-up work
I'm not sure to what extent the ballistae are necessary. But the 4 of them have been used every time to slow down the invaders, and reduce their numbers before they are dropped into the pit. Maybe once the pit population gets big enough, they can all just be dropped in without needing to be softened up first.
The armored undead siege troops are definitely the best addition to the pit. They make short work of the living who are usually a bit stunned from the fall. It's a bit hard to tell the zombies apart from the carnage now. The trolls stand out pretty well though.
One of the benefits to the pit, is that there is no cleanup. All the body parts, armor, and gore just drops into the pit with the zombies. Out of sight, out of mind.
With the pit trap now fully functional, the plan now is to establish some trading. But to do that, the surface needs to be tamed quite a bit. There are too many undead giant birds up there. When they're not murdering caravans, they perch high atop trees and scare away all the wood cutters who attempt to clear a safer path. And they don't path find into the fort like normal zombies or invaders, but are content just to occupy the surface. Stationing melee and marksdwarves right next to them doesn't even draw them down. I'm not sure how to deal with them really.