My last fort was a poured obsidian tower on an aquifer map. For the first few years my dwarves lived under the open sky with just thin wooden walls around them.
My first artifact was a steel chain mail. The immigrants and goblins just poured in after that. I don't kill dwarves on purpose, so most of them just stood around for years. I actually had a legendary peasant in that fort. Anyway I relied on an archer's nest above the main gate for defense. I don't use traps either for defense if I can avoid it.
I had one epic moment in it. A siege showed up, 3 bands, hammers, swords and bowmen. And they showed up on top of the cliff that stretched across the southern part of my map, overlooking my walls. I just knew if I let those bowmen get to the walls they'd slaughter my civvies.
So I sent out my axedwarves. I had been training them since the beginning, transfering any spinal injuries to the crossbows. I had 5 champions, legendary wrestlers, armor users, shield users and axedwarves outfitted in complete sets of masterwork steel plate, armed with masterwork steel axes. I sent them to the base of the cliff where the goblins would come down-- there was only one way down. The bowmen were the closest, so I hoped to dispatch them before the rest arrived. I would be quick and dirty and once the bowmen were gone I had no worries about the rest, even though the hammerers were led by an elite spearman, the last local ruler left alive in the goblin civ.
Well as it turned out, the spearman was a good bit faster than the leader of the other bands, the hammerers arrived slightly before the bowmen. There was nothing to do but charge, so up the ramp they went, straight into the oncoming invasion.
The bowmen unleashed a volley of arrows, and as they did so the body of their elite ruler went sailing over their heads, far into the forest behind. His head went the other direction, landing somewhere near my fortress walls. By the second volley all the hammerers were dead. There was no third volley. Lor, my first champion chased them all the way to the edge of the map, beheading left and right. There was not a scratch on any of my dwarves.