After losing two successive caravans, the elves showed up again. Learning from the last spring, and from the dwarf caravan fiasco, I mobilized the entire militia to cover their journey to my silver-domed trade depot. (It's a silver gazebo with gold statues on top. I am quite proud of it).
Sure enough, a vile force of darkness arrived. I properly activated the civilian burrow to bring everyone inside, and moved my militia to their positions, covering the elves. Once the elves were safely within the walls, I pulled back my military, keeping the melee fighters protecting the entrance, and the marksdwarves in the towers overlooking the entrance. I gave the order to raise the drawbridge.
The goblins charged towards the open entrance. They were peppered by bolts from the towers. A secondary force came up from the southwest, and were met with bolts from the Keep fortifications. After severely degrading the southern force, the Keep marksdwarves were reassigned to the guard towers to meet the remaining goblin melee fighters, crossbow goblins, and trolls. Within a short period of time, the remaining melee fighters were defeated, and either fled of lay dying. A small squad of cross-bow goblins remained under cover behind two unfished tower bastions. The front gates were opened, allowing the melee squads to finish the job.
The trading with the elves was completed. No outright deaths so far, however, one of the marksdwarves was wounded by a lucky shot when he was in an exposed position on the wall. One death was noted--that of a Trader. I am uncertain who the trade is, since he is clearly not my Broker.
Overall, a good result. Lessons learned include raising and fortifying the wall surrounding the entrance, creating a new squad of marksdwarves, finishing the tower bastions in front of the entrance, and building a new exit to the fortress to allow the melee squads quicker and easier access.
The goblins skeletons are piling up in front of the fortress.