How about a completely new mechanic... Instead of making them like Kuriotates settlements or cities. How about a new thing called Outposts. Outpost commanders make the fort act like a city in taking food to grow, have an upkeep cost, produce hammers, culture, and have religion and guilds, but only capable of building a small select number of military buildings and units. Maybe everything that it produces can be capped or have a set rate to further make them different than settlements. --- I think it would be better to have something new or just make no changes than to have them become kuriotates style settlements. Otherwise as the Kurios wouldn't everyone just spam forts everywhere?