A portcullis is a grille or gate made of wood, metal or a combination of the two. Portcullises fortified the entrances to many medieval castles, acting as a last line of defence during time of attack or siege. Each portcullis was mounted in vertical grooves in castle walls and could be raised or lowered quickly by means of chains or ropes attached to an internal winch.
There would often be two portcullises to the main entrance. The one closest to the inside would be closed first and then the one furthest away. This was used to trap the enemy and often, burning wood or hot oil would be poured onto them from the roof. Also, archers could shoot arrows at the trapped enemies. There were often arrow holes in the sides of the walls for archers and crossbowman to eliminate the besieging army.
A portcullis is a gate that can be lowered and raised to prevent entrance through an archway or gateway.