The portal allows you to connect your subs troops to your main city troops. Continuing the metaphor, I am sure they can go home through the portal afterwards right? So why canít you attack from the sub and have all troops from main city and all subs March from subs to the location? So if an enemy or monster you want to attack is across the map from your main city but two tiles from one of your subs, it should be a two tiled March from the sub for all your troops to attack.