View of the south gate, looking inward from the outermost tower. I guess the idea was that hapless invaders would enter an open or easily defeated outer gate and pour in to the first inner chamber. Next a much more sturdy or second gate or portcullis would be lowered, trapping the warriors. Next archers and other soldiers would attack the invaders from above, taking advantage of their attackers predicament. The process could repeated since it was necessary to pass four gates to get completely across the wall.