Came up with an interesting idea for an entrance defence scheme, after watching this video:
https://www.youtube.com/watch?v=e7pxKEG1o18While I was considering the best way to deal with any goblins that jumped from the traps into the pit trenches, it dawned on me that if a channel was dug as a ramp, i.e. gradually getting deeper and deeper each cut, like this in cross-section:
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then the dwarves doing the digging, as well as the dwarves collecting the goblinite, would have easy access to the trap.
The trap would also be reiterative, ie. the critters who jumped away from the trap into the trenches would fall further, the further they made it along the line of weapon traps; then any survivors would walk back up the ramp and along the line of traps again.
The trenches are covered by long, thin retractable bridges, for safety.
At the end of this setup I have a wooden door leading into another hallway completely covered by atom-smasher drawbridges, to destroy(hopefully) anything that makes it through the trap. When in the "off" position, the traders have access to the fort through this hallway.
All the bridges are hooked up to one lever, so in the "off" position there's no way for a dwarf to accidentally fall into the pit and the atom-smasher bridges are down, allowing access to the Depot in the fort.