Barbacan

Webster's Dictionary

(1): (n.) An opening in the wall of a fortress, through which missiles were discharged upon an enemy.

(2): (n.) See Barbican.

(3): (n.) A tower or advanced work defending the entrance to a castle or city, as at a gate or bridge. It was often large and strong, having a ditch and drawbridge of its own.

The Nuttall Encyclopedia

Or

fortification to a castle outside the walls, generally at the end of the drawbridge in front of the gate.