This patch gives fortresses a territory root, which means that if you lose your centre, you won't always lose your all other structures as a consequence. For comparison, centres, wonders, and several special structures already have a territory root.
See https://wildfiregames.com/forum/index.php?/topic/25352-should-fortresses-have-a-territory-root/ for poll and further discussion.
[EDIT] Also lowered the territory radius of the fortress by 20% (i.e. a 36% smaller areas).