That's an bellybutton wooping right there. Like Saintaw said, the AI is a bit dumb. When they attack my forteress, the first turn I attack them. I get a unit of town militia "500y" ahead of my gate. All the eni archers are going to waste their arrows on the unit.
While the AI does that, I put my 2 catapult units just ahead of the gate, and aim for the center row of grunts. When the catapult is too short, I hit the archers, when it's right on I kill many grunts, when it's too long, I kill the mounted general bodyguards ... including the general.
When the balistas are out of ammo, I do the same with my 3 units of archers, to soften the grunt units. The enemy archers are out of ammo by that time.
Lastly, I get my grunts/cavalery out. I put the grunts for a HO attack, bring my cavalery all the way around for a back attack, and a grunt unit on the flank.
The AI just looks at me. I order all the unit to attack at once, the eni often freack out and run.
