Tower (or Keep)The tower is a circular or square building, which was used as a lookout and for defence. The central tower in a motte and bailey castle was known as the keep. The height of the keep depends on how big the castle is, or how wealthy its owner is!
In medieval fortification, a bretèche or brattice is a small balcony with machicolations, usually built over a gate and sometimes in the corners of the fortress' wall, with the purpose of enabling defenders to shoot or throw objects at the attackers huddled under the wall.
Battlements were defensive parapets along the tops of castles. Battlements consisted of alternating raised spaces called merlons and the lower spaces called crenels. Battlements were created from stone and were originally designed to help protect the castle from invading forces.
moat, a depression surrounding a castle, city wall, or other fortification, usually but not always filled with water. The existence of a moat was a natural result of early methods of fortification by earthworks, for the ditch produced by the removal of earth to form a rampart made a valuable part of the defense system.
A bailey is the sturdy wall around a castle that keeps invaders out. The bailey of a medieval castle was usually built of stone. You might see a bailey — or the remains of one — if you tour a castle in England or France.
A motte-and-bailey castle is a European fortification with a wooden or stone keep situated on a raised area of ground called a motte, accompanied by a walled courtyard, or bailey, surrounded by a protective ditch and palisade.
A portcullis is a heavy castle door or gate made of metal strips that form a grid. A castle guardian might lower the portcullis to protect the people inside from an invading army. It was common during medieval times for castles to be protected by a portcullis or two.
An arrowslit (often also referred to as an arrow loop, loophole or loop hole, and sometimes a balistraria) is a narrow vertical aperture in a fortification through which an archer can launch arrows or a crossbowman can launch bolts.