Doing that requires coordination and a hefty amount of alliance resources (especially if your alliance is going to make a 2nd fortress which is what they usually do). Once your alliance is eligible to build a 2nd fortress you can build just like your first fortress but this time you need to place it strategically so that you can attack an enemy.
Ideally all of your members need to have Targeted teleport to be able to do this. Since you're going to teleport to an area without an active alliance territory.
Again do not do this if you can't get everyone in-sync.
Kingdom of Ephesus