The Price of Love

I've captured all the castles. I just can't seem to deal with 46 avatars, each of which has 15,000 hit points. They simply wipe out all my troops. I can't just sit behind the castle walls – with the very first volley, the catapult breaks through the castle gates and walls, and the avatars rush through the breach, and the slaughter begins. I can handle other troops without any problems.