yarr, i likes to do things without traps and bridges as well. though i do have either locked doors or bridges further back in the fort to totally seal off all the annoying dwarves who keep running out to the entrance, seeing the sun, then running back in again, then seeing a goblin and deciding to flee en masse out into the wide open world where i cant save them.
careful design means you can take down really big hordes with hardly any military dwarves anyway, once they have chain, leather and especially plate armor and shields with reasonable skills they are invincible, so long as they aren't equipped with spears.
and i remember flooding my very first learning fort with magma. i first thought that if i breached the magma pipe at the lowest z level the pressure would cause it to shoot up through my forts central stairway and incinerate everything, sealing all my dwarves in their rooms. once that didnt work i channeled out my magma forges, which were on the surface. i got so frustrated at the slow progress i sealed up all the magma again, which had only managed to melt some of the ore in my stockpile, and let it fill up a few large storerooms, then dug an up ramp from the level below, leading to my stairs. that was fun. i let water in the other end of my fort at the same time just for kicks.
seeing a dwarf wake up, go "oh my room is rapidly filling with water", run out into the hallway to escape and see a slowly advancing trickle of magma, then dance between the two till he has to choose one or the other way of dying was much more satisfying then something so diabolical should be. if you want fiery craziness either make a magma rezovoir high up somewhere, or make a lot of pumps.