I once ended a goblin siege by cutting a tree down into a pit.
Can you expand on this?
This was maybe my third or fourth siege ever, I had a twisty entrance into my dirt-hole of a fortress riddled with way more cage traps than necessary, and during a siege as usual goblins started getting caught. There's a bug where since an attacking group follows a leader during a siege, they path based off of the leader's pathing, and if you kill/cage the leader, the rest of the group will just sort of stand around. Well, I ran into this bug here, and there were about three goblins keeping me under siege, which was bad news because I was completely dependent on trade. I hadn't gotten into building military at the time, and didn't really have a good solid way of dealing with these goblins. I decided to try digging underneath them individually, and then I was going to dig a staircase down into a passageway where they would hopefully chase my dwarf and end up running into a line of cage traps. Unfortunately, a miner was brutally killed through my inexperience during this, and two of the three goblins left the map, bloodthirst quenched or something. The third disappeared from view, but I was still under siege, so I z'd him from the unit list and he was in a tree. I didn't really know how to handle things other than dropping them in holes at the time, so I designated a five or six tile wide channel to be dug around the tree with a single tile wide bridge going up to it on the opposite side of the tree that the goblin was standing in. There was no aggression from the goblin during this time, and my dwarves were not frightened, perhaps they cannot detect each other when tree branches are involved? I dug the channel fairly deep, maybe ten or fifteen z levels, and designated the tree to be cut down. The goblin fell down the pit with a bunch of logs, and to my surprise at the time survived the impact, with many injuries. Still being under siege and feeling pressure due to the upcoming potentiality of getting fruit from the elves which was very, very important to me at the time, I dug a channel from the stream to the pit the goblin was sitting in, ending the siege.
Dwarves before I learned how to set up a military/proper entrance traps was very rube goldberg.