Quote Originally Posted by Foz
You missed what I said earlier, and that is that the unit only becomes free upkeep if it can be recruited at the current location (we know this is the case because spear militia do not become free upkeep in a town until you build the building that lets the town recruit them). No city units are castle recruitable, ergo they can never be free upkeep there.
Ah, I see. I wasn't aware of that.