Correction. Unit strength isn't updated on the world map. They do grant the bonus in combat. I'm not sure about the fortification bonus though - unless that's just the same mechanism from Endless Legend. I imagine that bonus is only added if a castle is connected to a city? Or if separate from a city a castle have it's own fortification value. I wonder if you just ... make a bunch of castles together to build a choke point ... or a ... Great Wall? > . >