File under "One rule for the AI, another for the Human Player".

One of my cardinals came across an aptly named Byzantine general, Prince Vlasios the Mad, besieging rebel held Smyrna. Nothing unusual in that except it was with just 2 units of heavy cavalry, a ladder and a ram, miraculously occupying the fort with the same force the following go, 2 turns before the defenders had to sally or surrender.
I took a screenshot of the assaulting force's chart but Imageshack is out to lunch or something at the moment.

Is there some way I can dismount my heavy cavalry or train my horses to climb ladders and use battering rams?