Easily Defensible Gate
The two gates leading up to the main entrance of the castle made it easy for defenders to hurl rocks, burning pitch and offal on to any attackers dumb enough to try to make a frontal attack on the castle. As far as I know, nobody ever made the attempt. In fact, most of the castles we've seen in Europe were never involved in an actual battle. The ones that were are the ones that are now gone.