This is one of the many Helm's Deeps.
I know, but I think this one is pretty good. It doesn't include any AI file, but there are enough good files on this site.
You have the command of Rohan, you must hold on until aid comes from the Westfold army. You are outnumbered, but the fortrees provides excellent defence. Watch out for their 'suicide bombers' and the attacks on your walls. The only weak points of your defence are the gate of the Hornburg and the place in the Deeping Wall where the water from the Deep streams out of the fortress.
This should be played at hardest, else the enemy won't do anything. I have a Minas Tirith, that seems to be suitable for a campaign including the Pelennor fields battle.
I would like to see comments posted so I can become better at this.