My last fort had the greatest battle I have ever had in dwarf fortress.
I counted - 182 enemies, thanks to the fortress defense mode. Most of them in the late tiers. After two years of endless battles, sieges, ambushes, I had closed my fortress. Of the fifty steel-clad fully legendary dorfs, 26 remained. 24 others were just starting their training - ¾ of them were still novice in everything. After a sad error in lever linking, I opened my fortress and poured magma on that lever. Not my finest moment.
After an epic battle, I ordered the retreat. There was 156 dwarfs before the assault - after the battle, 78 remained. Nearly all of them made it to the bunker, only a dozen or so were killed while they were going. I made a review of my troops - no soldier was still alive. They had all died trying to make it to the gates to give a chance to my masons who needed some time to wall the fortress off. I passed to plan B. Digging to the gates, I sent my dorfs to loot the bodies of those who died there - friends and ennemies. I quickly retreated, equipped the survivors... And I attacked.
I was surprised the dorfs survived. I guess the other army had been really damaged by the battle of the gates. Anyway, 13 dorfs were still alive, I was about to restart production of food and booze and everything was happy and I realized half of the fortress was covered in magma. The original magma flow that the lever had unleashed - it was'nt stopped, because the drawbridge I built to block it was never linked to the lever!
/facepalm.
All the remaining dorfs died, if you wonder: all the useful piles (wood, stone...) were under the magma and I could'nt make walls.