arrows from castles, details please

[zlefin]

i couldn't find any suhc info in the domdb stuff. at least not in the forts section.
while it may not be a big deal, it does matter some, so i'd like to know. in particular, if a fort is gonna have a significant number of arrows on defense, i'd make a point of always having a commander to defend it for a few rounds. also, it matters a good deal if your fighting a nation that's bad at taking the choke point of a castle.