I noticed that ports can have walls on the campaign map as they are upgraded--which implies they are fortified. This made me start thinking--what if you could garrison ports with armies like you can cities or forts? The more I thought about this, the more I figured that this could add a lot of strategic depth to campaign maps. Blockading or besieging ports could cut off the enemy's trade flow, but perhaps capturing them in battle (through a siege) and garrisoning them with your troops could result in plunder at the enemy's expense.