A vile force of darkness has arrived!
I never thought I'd say this, but I'm glad the elves made it inside first. They brought me a Tigerman, a Giant Tiger, and two more Giant Lions among random monkeys and such. I accidentally offered them a barrel though, so I had to seize them as well as the wood the elves were carrying. Hopefully they still bring me nice things next year.
As regards the siege, there was a squad of trolls which spawned to the southeast and my crossbow squad tore to shreds from the walls. There is the Polo squad (hammergoblins mounted on various beasts), a lancer squad (mounted pikers) and a Mongol squad (mounted archers). These squads all spawned on the north side of the river, went straight south and had their leads amphibious mounts jump into the river, where the elites quickly drowned. Now they are all just standing there on the north bank looking slightly confused, and I am more than happy to leave them there since I don't expect another caravan until the dwarves make their autumnal visit. Not to mention that, including the mounts, my dwarves are vastly outnumbered and would have to attack across the bridge where they would be flanked on one side by horrible monstrosities with pointy things and on the other by horrible monstrosities with flying pointy things.
Interestingly enough, the western edge of the river is where it flows off the map, and a wide swath of the river is only 3/7 deep at that position. The Hammer Lord was swept off his mount but made it to shallow water, meaning he is still alive but with no way out of the riverbed. I think at this point I can let my dwarves go down to green alert, which restricts them to the fortress, caverns, and southern bank, but I'll have to keep an eye on the situation as it develops.
Imiknorris, please tell me your map is on fire now.