You have 6 gates, and usually, all of them ae destroyed and you have to fight it out in the keep.
As the enemy "Gate Hops" you have to retreat your archers and crossbowmen. There's pitch inside all the walls, so you can keep the number of swordsman down.
A whole half of the map is blank because I spent 6 hours on the castle!
EDIT: OK, I've been inactive here for a while.. but... I've changed the landscaping, updated the invasions, and the enemy actually attacks now.