Cavalry and sieges?

[PBI]

Yep, cavalry can only get in through the main gates or through a breach in the walls if you have siege artillery to knock them down. Cavalry really aren't much use in sieges, they don't have room to maneuver, they don't have the numbers to soak up losses, and worst of all they have trouble charging properly in the narrow streets. And yes, they can't do anything about enemies on the walls.

Only real use for them is for shifting the balance of a tough infantry fight for the gates or a breach in your favour. Move your cavalry through the enemy soldiers to the empty space beyond (make sure you keep renewing the move order so they don't get bogged down fighting the enemy infantry), then turn them around and charge back into the enemy rear. You will lose a lot of horsemen this way, but the payoff is that the more you lose, the more likely the survivors are to be able to charge properly (in a way, a unit of 10 horsemen is more useful in a siege than a unit of 30). But even if the charge doesn't work it'll help by having the enemy infantry be forced to fight an enemy behind them as well as in front, hopefully causing a rout and saving you from a long and costly fight to wear them down with just infantry.

Ultimately though, cavalry are not very good in sieges. The payoff is their dominance in the field, where the roles are reversed: In the field cavalry is the most effective arm while heavy infantry is useful only in a limited role, the opposite of the situation in a siege. Siege assaults are largely about bringing the right troop mix. Bring lots of heavy infantry and enough siege artillery to make at least one breach (generally one trebuchet/cannon, or two catapults) and you can't go too far wrong, just don't expect to be winning any siege assault against a reasonably well defended settlement by huge margins.

Spoiler Alert, click show to read: 

Of course, if you are willing to go over to the dark side, there is an exploit you can use to take cities using cav very cheaply: Attack with a stack of only a few units of cav; with such an apparently weak besieging army, the defenders will sally. When they do, lead them far outside the city and then lead them on a wild goose chase until they are exhausted. Then run your cav in through the open gates and hold the centre square for the two minutes needed to win.

Bear in mind though, that every time you use this exploit, a puppy dies. Not to mention it will ruin the game.