question on castle storming

[Foom]

Merry Jolkar said:
Thank you.

One point is still not clear to me:

When you say, "Anybody set to break siege will fight in the same battle as anybody moving in from an outside province."

will this battle take place outside the castle in open land, or will the defenders somehow sneak past me, and defend from within the castle?

The battle takes place outside the castle. The guys breaking siege all run outside and join whatever friendly forces are moving into the province that turn.