Nay! Siege is about capturing a flag inside the castle, with one team starting in the castle defending it and the other outside the walls trying to get in and capture it.
We have so many battle maps with ruins and such, but none with actual walls to fight on. The point of adding these maps isn't making one party walled off from the other, rather it's about adding another level to fight on. We have two maps that do this as of now. Both of them set in a city. If you don't like castles, I can make some mountain maps, which would function in the same way. Though, mountain maps discriminate cavalry.
Goes without saying, that they wont match the quality of these.