Fair point on the castles kniteowl, it's a tough one, perhaps they could suffer a loss of there def bonus's with steel an the economic bonus's of trade routes with economic's, yet with the discovery of later tecks, say flight (which paved the way for the modern tourist industry), they could gain new ones to represent there role in the modern era of tourist attractions an places of historical/cultural significance? A bonus of some extra gold or trade coins + culture representing modern tourism with the discovery of flight?, so all those old castles now generate wealth an culture in the modern era which ties into there current real life roles