This is the gate that grants access to the upper enclosure of the castle.
If you think back on your ascent to this point, you can appreciate the sheer effectiveness of this defensive system. You have walked up a long ramp where an attacker would have been constantly exposed to fire from the top of the walls.
An invading army would have had to breach two gates during that climb, only to face this final obstacle.
Apart from its solid construction and the defensive openings above, its curved design makes it exceptionally secure: on one hand, it slows down horses, and on the other, it prevents attackers from seeing what lies ahead or firing directly inside. Instead, invaders become easy targets for the defenders the moment they turn the inner curve of the gate.