Indeed, forts take away neighboring provinces resources depending on the admin value of the fort (so, admin20 castle will take 20% and admin 50 fortified city will take 50%), so two neighboring fortified cities would deplete all the resources of one province.
Indeed, forts take away neighboring provinces resources depending on the admin value of the fort (so, admin20 castle will take 20% and admin 50 fortified city will take 50%), so two neighboring fortified cities would deplete all the resources of one province.
Does that take 50% of the halved resources or 50% of actual resources? Meh, it's been a while.