The Writer’s Guide to Castle Defenses
Castles have been romanticized for centuries, to the point where we forget their use. First, they were a home. Second, they were a series of carefully designed kill zones.
Today I will cover the features most seen in castles and their purpose. I will limit this article to medieval Europe since that is when and where most castles are located and because that is where most of my knowledge lies.
As always, magic is the exception to the rules. Because magic.
Keep – A keep was a fortified tower or building. It was in the most defensible part of the castle. It was as a home for the residing lord, his family, and household.  In most early castles, the keep consisted of only a few rooms. Sometimes only a screen would separate the Great Hall from the lord’s bedroom.  However, as castles became bigger and more complex, the keep became larger. Later castles had buildings ringed around a central courtyard or enceinte instead of a single keep.  In motte-and-bailey castles, the keep is set on top of a motte, an earthen mound.
Within the keep was located the Great Hall, a large room used for greeting guests, feasting, social gatherings and meetings, and legal trials.
Bailey or Ward – The bailey or ward is an open space enclosed by a curtain wall. All castles have at least one. Its primary function was to leave invaders exposed to attack from the keep and battlements. Baileys often contained buildings such as barracks, stables, kitchens, storerooms, chapels, and workshops. The well was also in the bailey. As castles became more complex, they used a series of baileys for protection. The central bailey was called the inner bailey, the further out, the outer bailey. A bailey off to one side was called a nether bailey.
Curtain Walls – Curtain walls surrounded the baileys. A typical curtain wall was 10 feet thick (3 m) and 39 feet tall (12 m). They had to be tall enough that it was difficult to scale them with ladders and thick enough to withstand bombardment from siege engines. Besides going over or through, curtain walls were vulnerable to tunneling, known as sapping. The sappers would either tunnel under the walls, coming up inside the bailey, or create a void under the wall, causing it to collapse.
Gatehouse – A gatehouse was a fortified entrance. Because of the vulnerability of the gate, they often had flanking towers that stuck out further than the gatehouse, allowing the defenders to fire upon attackers.  The gates opened outward, so that anyone trying to force them in would work against the hinges. Most gatehouses had at least two sets of gates. Heavily fortified gatehouses were known as barbicans.
Portcullises were heavily latticed gates that were opened by being raised vertically. Their chief advantage was that they could be closed quickly by a single person. They were often set inside the gatehouse, behind the outer set of gates. They could trap attackers inside the gatehouse.
Moat – Moats became a popular way to protect curtain walls. They could be dry or filled with water. Moats were crossed either by a flying bridge or a drawbridge.  Moats were not limited to the outside of a castle. Some castles have moats inside the curtain walls, protecting the keep, for example.
Postern – A postern gate or door was a small, hidden door in the curtain wall that allowed people to sneak in and out of a castle. During a siege, messengers or soldiers could leave and enter without the knowledge of the attackers.
Battlements are defensive architecture built into curtain walls and towers. The most familiar type of battlements are crenelations, the tooth-like structures of alternating spaces. The upright part is called a merlon with the space called a crenel. Merlons were the height of a person and provided cover from incoming fire. Crenels allowed archers to fire back.
Machicolations were battlements that extended beyond the top of a curtain wall or tower, creating an opening through which stones, hot sand, and other nasty surprises could be dropped on people at the base of the walls. 
Arrow slits, also known as loopholes, were vertical openings in outer walls that archers and crossbowmen used to fire on attackers. The walls were angled on either side of the opening, providing a wide field of fire.  Plus, the narrow slit was a small target, protecting the archer inside.
Murder holes were similar in function to machicolations, except they were in the ceilings of gatehouses or buildings. Boiling water, hot sand, or stones could be dropped onto invaders.
I hope this was helpful. Let me know if you have any questions or suggestions by using the Contact Me form on my website or write a comment. I post every Friday and would be grateful if you would share my content.
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Copyright © 2021 Rebecca Shedd. All rights reserved.
 Cathcart King, David James (1988). The Castle in England and Wales: An interpretative history. London, UK: Croom Helm. ISBN 0-918400-08-2.  Barthélemy, Dominique (1988). “Civilizing the fortress: Eleventh to fourteenth century”. In Duby, Georges (ed.). A History of Private Life: Volume II · Revelations of the Medieval World. Cambridge, MA: Harvard University [via] Belknap Press. pp. 397–423. ISBN 978-0-674-40001-6.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.  Cathcart King, David James (1988). The Castle in England and Wales: An interpretative history. London, UK: Croom Helm. ISBN 0-918400-08-2.  Jaccarini, C. J. (2002). “Il-Muxrabija: Wirt l-Izlam fil-Gzejjer Maltin” (PDF). L-Imnara (in Maltese). Ghaqda Maltija tal-Folklor. 7 (1): 17–22.  Friar, Stephen (2003). The Sutton Companion to Castles. Stroud, UK: Sutton Publishing. ISBN 978-0-7509-3994-2.
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