I had a reasonably successful fortress, 5 million in created goods, over 100 gold barrels, bins, chests, door (100 each!). the local rinocoress population provided ample food, (my legendary cook made 600 meals in a single season some valued over 100,000) ample alcohol. 3 full contingents of military dwarfs out fitted as such
steel helm
steel caps x2
steel breastplates
steel mail shirts x3
steal gauntlets
steal greaves
steal high boots
steal shields
steal axes/spears (one division of 10 axe dwarfs, one division of 10 spear dwarfs), the dwarfs were trained to legendary pump operators (and some were even high master or legendary wood cutters). there skill was modest but they managed to slaughter a cyclops with no casualties, and wipe out my first siege while only losing one of the new recruits. then my second siege came.
I stationed my dwarfs at the choke point entrance of my fortress, the goblin axe men came, there trolls kicking in my gold doors in my dwarfs charged, 4 or 5 injuried, no deaths, 20 goblins killed goblin legs, hands and feet and equipment strung out at the entrance to my fortress now covered in blood. I think "whew that was close", the last goblin is routed, wait it still says siege, crap there must be another division, well this sucks my military power is almost halved, , and I am not making this up latterly 2 more full pages of nothing bot goblin bowmen and cross bow men. My dwarfs fought valiantly, even getting or two of the buggers, but the rest were mercilessly shot down.
what could I have done? I had a choke, to limit the range my dwarfs could be shot at I had 2 full contingents of dwarfs in full steel armor made by a legendary armor smith. weapons made by legendary weapon smith, and 3rd contingent almost ready but still waiting on gym training to finish. heck i even ordered my army to go about and kill the local wild life to improve there skills at a faster rate than training would allow, not to mention most of my dwarfs got to competent level just form fighting the colossus.