Do you get double the reward if you hold 2 of these castles?
Edit: After taking one of these I left a small garrison there to defend it, which got wiped out by a much larger army 237K worth of mages but instead of him capturing the city, in the battle report I saw "Action failed. You have reached maximum city capacity." and I ended up keeping control of it.
not that I'm complaining or anything, just found that curious