There are 18 forts in the game, and they all are played in 3 rounds. Here is the list:
Legion Forts: -3, -2, -1, -1
Dinary Forts: 1, 1, 3, 3, 5, 5, 6, 6
Unwary Forts: 2, 2
Signal Forts: 4, 4
Tax Collector Forts: 8, 8
So, seeing round 2, you can already tell, what forts will appear in round 3.