I'm using Dig Dwarfier, so naturally the siege was of the Orcs, and in the second summer when I had around 33 dwarves. I immediately ordered all my dwarves inside and to retract the drawbridge. Sadly, maybe a little more than 1/4 of my fortress was in a tunnel leading to the magma pipe, which was not connected to my main fortress, so they were stuck out there the same as the Orcs. Being the complete idiot that I am, I thought I could open my bridge, and get my dwarves in before the Orcs descended on them with hammer and wrestling. I was wrong. The Orc force had a LOT of wrestlers, and maybe a little under 2/4th of them got in, along with an Axeorc and a couple Hammerorcs, before I closed the gates. In desperation, I started screaming 'WEAPONSPREE' as I went to the military screen and activated every single dwarf I had. I went along screaming weapon spree while the experienced orcs battled my rag tag group of recruits and one axedwarf and marksdwarf (From my hunter and tree-feller). Many of the dwarves in the fortress died in the first 45 seconds of the engagement.
Then, I finally noticed something that started even before the siege started: A fire golem climbed out of the magma pipe and started brutally murdering some of the dwarves stuck around the magma pipe and in the tunnel leading to it. I watch as it murders one of my blacksmiths stuck around the magma pipe. Now, the rest of the Orcs that didn't get in before I retracted my bridge get into the tunnel and murder the rest of the dwarves there, and they conveniently get into the magma pipe room just as the fire golem goes into the safety of the pipe.
I'm still screaming WEAPONSPREE as the Orcs in the fort battle the dwarves in the fort, reducing the dwarven numbers to fourteen before all the Orc's die. A tantruming dwarf then pull the lever to the bridges, and as I go 'Fuuu' a few more wrestlers get in. I disactivate one recruit, which turned out to be a gemsetter, and order that dwarf to pull the lever. The dwarf thankfully does so, only letting around 3 Orcs get in, and then bleeds to death. The wrestlers somehow manage to reduce my numbers to 5 until they are taken out, and 2 of that 5 promptly bleed to death.
The 3 remaining dwarves go to rest - one of them repeatedly throwing a tantrum - and I'm breathing hard, staring at the screen. I think its finally over until I see a goblin thief appear as a chicken spotted him. On the fortress side of the moat. While I contemplate how the goblin got past the moat, it proceeds to steal a few plump helmets, then go stab one of my 3 dwarves to death in his sleep, and then go steal some masterwork crafts. While I curse myself as I watch the 2 dwarves rest, one continually tantruming, and a dwarven corpse lying in bed. Suddenly, I get the notification that something has pulled the lever, and I pause and go look there, just in time to see a fire snake making its way off. I stare gaping at the screen as the Orcs rush in and kill my final two dwarves. I then commence cursing as I get the game to the title screen.
So, any tips on how to stop this from happening again?