* Thick Walls: The Tower of London's walls are up to 15 feet thick in some places, making them extremely difficult to breach.
* Towers: The tower is surrounded by 13 towers, which were used for defense and observation purposes.
* Moat: The tower was once surrounded by a moat that was up to 12 feet deep.
* Drawbridges: The tower's drawbridges allowed the inhabitants to control who could enter and leave the castle.
* Portcullises: Portcullises are heavy iron grates that could be lowered to block the entrances to the tower.
* Murder Holes: Murder holes are small holes in the ceiling that could be used to drop hot liquids or objects onto attackers.
* Battlements: Battlements are crenellated walls that provided defenders with a protected position from which they could shoot at attackers.
* Arrow Loops: Arrow loops are narrow slits in the walls that allowed defenders to shoot arrows at attackers.
* Machecolations: Machecolations are projecting parapets that allowed defenders to drop objects on attackers below.