Sieges of coastal forts/Sea lines of communication

[random_name_euIV]

Coastal barrages and marines were an important addition to the naval side of the game. They are however only beneficial for attackers and I would suggest benefits for defenders too. My idea is to make unblockaded forts way harder to capture, representing the long sieges of Candia or Ceuta and longivity of trade cities of Portugal or Venice. This bonus might be restricted by a trade policy (for example replacing “Improve inland routes“ for non inland trade nodes by something like sea lines of communication). This would make naval game play more important both for a defender (keeping trade up and/or provinces unblockaded) and an attacker (destroying trade fleets and blockades). It would also put naval/maritime focused nations on a more equal footing with land powers without beeing limited to islands.

Edit: The bonus could also be tied a combination of forts, ramparts, coastal defeces, and trade company investments.