I made a lava cannon directly over the entrance to my fortress this one time. Unfortunately due to an oversight with the order in which I rebuilt it after taking it all apart to make some modifications, I got slaughtered by goblins before ever getting to use it on them. I did fire it on a human caravan though. Good stuff. The contents of the trade depot went up in a very satisfying poof of smoke. Two of the humies survived, limping away and trailing blood. Because living things in DF aren't aware of the danger that fire poses, however, they limped back toward the depot after recovering their wits, directly into a brush fire. Suffice to say, they both burned to death. This was well after the fortress started to spiral downward into dysfunction after the goblin siege however. Shortly after this a breach in the system that fed the cannon from its adjacent volcano occurred, and the fortress slowly flooded with the blood of the mountain. One of the images of that fortress that stands out in my mind was my mayor and another dwarf whose guts were trailing behind him getting into a fistfight on top of a hospital bed, and a berserk child killing several other dwarves in my dining hall.
