I cannot kill Rohen. Is there some trick to it?
Well you can't kill him before aliyah (or something) comes barging in with reinforcements.
I used a lot of ranged fighters throwing ice rocks at his face.
I was playing a heavy warrior avatar so i could stand ground while the hurlers pounded the dino's. Then rohen can be killed the same way.
Make sure you use the H-button to avoid half of your army wandering around during the fight.