What I am almost completely sure that they`ve done is to reconstruct the entire campaign map close-up in 3D. The only thing that is different from time to time you play is ports and roads.

I`ve fought against relief forces outside Tarentum 3 times, and all times the battlefield looked exactly the same. Also when I fought a siege battle at Tarentum I could recognise the relief battlefield not far from the settlement, wich was a cool experience since I had got so used to fight battles down there and knew the place very good.