How Castles Work

When you think of the Middle Ages, you might imagine knights, lords and ladies, jousting competitions and bloody battles -- probably taking place in or around a castle. Castles were important staging points for conquests and defenses of territories in medieval times. The designs and constructions of these fortresses varied greatly, and many survive today.

The Merriam-Webster Collegiate dictionary defines a castle as a "fortified group of buildings" [source: Merriam-Webster]. But a more practical definition is that a castle was a fortification of the High Middle Ages (10th to 15th century) equipped with high walls, towers and a moat. The word "castle" comes from the Latin word "castellum," which means "fortified place." The French popularized the term "castle" in the Middle Ages.


Castles served a primarily military purpose -- they housed armies and acted as garrisons that controlled a particular territory. Many castles were part of fortified towns and sheltered the surrounding villagers in times of war and siege. As time went on, castles also became residences for lords and kings. Near the end of the Middle Ages into the modern era, castles lost their military function and either functioned as residences for the nobility or were abandoned altogether.

In this article, we'll examine where castles came from, how they were constructed, how they were used, how they were attacked and defended, and what became of them.

History of Castles

The ruins of Urquhart Casle in Scotland
Medioimages/Photodisc/Getty Images

Castles evolved from ancient walled cities like Troy, Babylon, Jericho and Mycenae. These cities had thick, high stone walls with gates that limited traffic flow. Soldiers would stand guard at the gates and on the walls to fend off attackers.

The earliest type of castle was essentially a ringed fort called a grod. A grod consisted of wooden and earthen walls (ramparts), a fortified gate or gates and a surrounding moat.


A second type of early castle stemmed from the high, round watchtowers that the Romans built along their frontiers. The tower, called a bergfried, was made of wood (and stone, starting in the 13th century). Bergfrieds, found throughout Germany, were the predecessors of the tall towers in later medieval castles.

The third type was motte and bailey castles. They consisted of a mound (motte), which was located within an open courtyard (bailey) that was enclosed by wooden wall with a fortified gate. On top of the motte was a wooden tower called a donjon. The motte and bailey castle incorporated features of the grod and the bergfried. They became popular during the reign of Charlemagne in France (A.D. 800) and were used widely by William the Conqueror after the Norman conquest of England in 1066. The motte and bailey could be constructed in a matter of weeks or months.

These early castles laid the foundations for developments of castles in the High Middle Ages.

  1. Stone and brick walls replaced wooden ones. Stone walls were sturdier and could be built much higher.
  2. In some castles, an inner wall was added, forming a concentric ring. This extra wall provided more defenses.
  3. The bailey became larger and divided into separate courtyards.
  4. The donjon became larger and made of stone -- and its name changed to the keep.
  5. Other buildings were added in the baileys -- like great halls, palaces, chapels, residences for knights and servants, stables and workplaces for craftsmen.
  6. Several large, tall towers were built into the castle. Some towers were incorporated into the outer walls, while others were freestanding structures within the courtyard.

We'll learn more about these features on the next page.

Castle Features

Edinburgh Castle in Scotland was built high on bedrock, so it didn't need a moat.
Nicolas Asfouri/AFP/Getty Images

Remember that castles served primarily as housing for military forces -- they evolved into residences for nobles. So, they were designed for defense. Medieval castle builders incorporated designs of early castles and improved upon them over time. Castle designs also changed to keep up with improvements in siege technology. Castles also had to provide necessities for living (like sanitation, fresh water and cooking areas), which were especially important when the castle was under siege.

With this in mind, let's look at the major features of a castle.


  • Outer defenses
  • Moat
  • Walls (inner and outer)
  • Towers (inner and outer)
  • Gatehouses, drawbridges and barbicans
  • Inner defenses
  • Baileys or wards
  • Living quarters and support buildings
  • Keeps or donjons
  • Great halls
  • Chapels
  • Stables
  • Wells
  • Workshops

Outer Defenses

The moat -- a large ditch or trench surrounding the outer castle wall -- was a castle's first line of defense. The moat could be filled with water or dry (a dry moat could have been lined with wooden spikes). It usually had a drawbridge across it that was drawn up when the castle was under attack. Many moats were also dump sites for garbage and sewage.

The existence of a moat was dictated by the terrain -- not all castles had moats. Some castles were built high up on bedrock and didn't need them. Edinburgh and Stirling castles in Scotland, for example, stand on high rock outcroppings. Many German castles along the Rhine River were built on the mountainsides of the river valley.

Outer Walls

The outer curtain wall was high, thick and made of stone or brick. Walls could range from 6 to 10 meters high and 1.5 to 8 meters thick. In many castles, wall thickness varied according to the area's perceived vulnerability.

Curtain walls were actually two walls. Masons cut and fitted the stones or bricks of each wall and cemented them together with a limestone mortar. The builders filled the spaces between the walls with stone fragments, small rocks and mortar fragments (rubble). As the wall grew higher, the builders placed wooden scaffolds or work platforms into it so they could work and bring materials up using man- or animal-powered cranes or ramps. When that particular section of the wall was finished, they tore down the scaffolding, but a square hole remained where the scaffold's support beams had been.

Some castles had a substantially higher outer wall called a shield wall. The shield wall was often placed on the side of a castle that might be especially vulnerable to siege weapons like catapults, trebuchets and siege towers (more on this later). The shield wall could also prevent objects from going over the walls into the bailey.

Most outer walls had battlements on top, like:

  • Crenellations: Rectangular blocks alternated with openings across the top of a wall or tower. Soldiers could hide behind the blocks and shoot through the openings.
  • Walkways: Some walls had walkways built into the stone, while others had wooden walkways on the inside of the wall where soldiers could stand guard and defend the walls during battle.
  • Hoardings: Covered wooden overhangs that ran along the top of a wall. The French later used stone hoardings called machicoulis. Hoardings had holes in the flooring from which soldiers could shoot arrows or dump various objects (rocks, hot tar, boiling water, hot oil) on attackers.
  • Breteches: Small, overhanging rooms on French castles, similar to hoardings, that jutted out from the wall. Breteches were made of stone, had windows or arrow loops, and also had a floor opening. A breteche extending above the top of a wall was called a bartizan.
  • Arrow loops: Narrow slits or openings in walls and hoardings through which archers and crossbowmen could fire arrows. Many arrow loops were wider on the inside and tapered toward the outside of the wall; this design gave the archer a wide field of view.
  • Embrasures: Rotating cylinders with an arrow loop that were built into the wall or tower and could give an archer a very wide field of view.

On the next page, we'll finish up with the outer defenses and move on to the castle's inner defenses.

Castle Defenses

The portcullis on Bodiam Castle in England
Photo courtesy


These tall, round or square structures were built into the length or corners of the castle walls. They were usually higher than the walls and constructed in the same manner. Rounded towers projecting out from the wall or at a corner gave a better view to the defenders. The walls usually had arrow loops, and the tops could have hoardings or be crenellated or roofed.

Inside the towers, stairs were often circular (turning clockwise while going up), narrow and made of wood or stone. This clockwise turn gave the defender an advantage because soldiers were right-handed (left-handed people were considered evil, so even if you were left-handed, you learned to fight with your right). Going up the stairs, defenders had room to swing their weapon hands, but descending attackers could not do this easily.


Gatehouses, Drawbridges and Barbicans

Gatehouses were inside the wall and connected with the bridge over the moat, but they were more than just doorways. The gates were usually long tunnels with arrow-looped towers at either side of the entrance. The outer opening of the gatehouse tunnel was covered by a grated wooden or iron gate called a portcullis. Soldiers could raise the portcullis with a winch and lower it while under attack so defenders could shoot arrows through the openings.

In the ceiling of the gatehouse tunnel, there were openings called murder holes through which defenders could drop objects and hot liquid. The sides of the tunnel also had arrow loops. Finally, the gatehouse had a heavy wooden door at the inner opening, which soldiers could shut and lock with braces.

The bridge's retraction mechanism was usually located inside the gatehouse. Some drawbridges were raised and lowered with a winch, and some had a center fulcrum that allowed them to pivot perpendicularly to form a wall. Other drawbridges could spin out so that they were parallel to the moat and did not connect to either side.

Some bridges had an additional fortified structure in front or alongside them called a barbican. The barbican was built of stone and had towers with arrow loops and battlements.

Inner Walls and Towers

The inner walls and towers were constructed much like the outer version. They had many of the same features (arrow loops, hoardings, crenellations) and served the same purpose. The inner walls also divided the bailey or ward into different sections. In some castles, the inner towers were freestanding structures.

A knight readies for a joust at the Tower of London.
Peter McDiarmid/Getty Images

Bailey or Ward

From a military standpoint, the bailey, or courtyard, was a wide-open space. So any invading soldiers who made it through the gate into the bailey would be exposed to arrow fire from the outer walls and towers and the inner walls and towers.

The bailey also served as a marketplace for festivals and fairs, a practice field for drilling soldiers and training horses, and an area for tournaments. In the tournaments, knights fought with swords and shields on foot and jousted in arenas called lists (or list fields). In the later Middle Ages, baileys featured gardens and fountains.

Some castles didn't have inner walls, so the bailey also contained the towers, the keep (main residence) and auxiliary buildings (great hall, chapel, knight and servant quarters, kitchens and workshops).

Inside a Castle

The great hall in Warwick Castle
Photo courtesy Warwick Castle

The keep and the auxiliary buildings that supported castle life varied from castle to castle. Sometimes buildings (like the chapel, great hall and kitchens) were integrated into the keep, and sometimes they were separated.

The keep was the main residence of the ruling lord. It was made of stone and could be square or circular. Keeps could be attached to walls or freestanding. They had many functions.


Residential apartments contained beds and furnishings. They were usually heated by fireplaces, and light came through glass windows.

The great hall could be located in the keep or in separate buildings. In the earliest castles, like the one described in the epic poem "Beowulf," great halls were used for eating and sleeping. Later, they were used for entertaining and holding court. They usually had high ceilings and large fireplaces. The floors were usually stone or dirt.

Storage of food, beverages and gold was usually in the lower levels of the keep.

Defense (arrow loops, armory, battlements) usually occupied the top levels.

Prisoners were kept in the dungeon (derived from "donjon"). Dungeons were usually in the upper parts of the keep because it made escape more difficult, but they were later moved to the lower levels.

Wells, like this one at Bodiam castle, were essential to the survival of a castle.
Photo courtesy

Religion was important in everyday life during the Middle Ages. People went to church every day, usually morning mass. Most castles had their own chapels and priests, either in-residence or visiting. Chapels could be simple rooms in the keep or elaborate separate buildings.

Horses were essential in medieval life. Knights rode them into battle. They pulled carts. They were transportation, like your car. So they needed a garage -- or stables, which were usually located in the bailey.

Because of the threat of fire, kitchens in early castles were separated from the keep in kitchen towers. As brick construction became more common, castle designers moved kitchens into the keep.

Wells and cisterns were collected water for the castle. Often, the ability to access freshwater was a key factor in whether a castle could withstand a siege. Wells could be located within the keep or in the bailey. Cisterns collected rainwater from the roofs. Some castles had rudimentary plumbing that channeled water from cisterns to sinks.

Castles needed many craftsmen and artisans, including carpenters, farriers and blacksmiths, to maintain the buildings and grounds. Their workshops were usually separate buildings within the bailey.

Castle Construction

An aerial view of Warwick Castle
Photo courtesy Warwick Castle

Castle construction was an expensive undertaking; King Edward I nearly bankrupted the royal treasuries by spending about 100,000 pounds on his castles in Wales. Castle building employed about 3,000 workers (like carpenters, masons, diggers, quarrymen and blacksmiths) under the direction of a master builder (Master James of St. George built the Welsh castles of King Edward I). Castles generally took two to 10 years to build.

To learn and understand medieval castle building techniques, let's look at a modern castle building project. As an experiment in archaeology, Michel Guyot and Maryline Martin have assembled a team of 50 workers (architects, archaeologists and skilled workers) to build a medieval castle from scratch by using techniques and materials of the Middle Ages. The project, in Treigny in the Burgundy region of France, is called Project Gueledon. The design is based on 13th-century castle architecture -- it consists of a dry moat, curtain walls, corner towers and a large tower keep. Construction started in 1997 and is expected to last about 25 years. After the initial investment, the cost of the project has been covered by tourism. In 2006, the site hosted more than 245,000 visitors, and the project brought in about $2.6 million.


The building materials are stone, clay soil and oak trees that are found near the site. The workers use traditional techniques from the 13th century. To split stones for the walls, quarrymen "read" the rock face to see the lines where it will fracture. They then drive a line of holes into the stone and then pound corners into the holes, which makes shock waves go through the stone and break it.

Workers use horse-drawn wagons to haul the stones from the quarry to the building site. Stone masons then chisel the raw stone into blocks. Workers use man-powered cranes to lift the finished stones to the scaffolding on the castle wall.

Other workers make mortar on the site from lime, soil and water. The masons on the wall fit the stones together and use the mortar to hold the blocks together.

Workers use traditional tools to measure and lay out castle pieces. For example, craftsmen use a long rope with knots placed every meter to measure wood beams and layout pieces. They also use wooden right angles and calipers for measurements. They use a wooden triangle with a line and plumb bob suspended from one angle as a level when placing stones.

As the castle wall gets higher, new scaffolding must be placed in the wall and the old ones removed, leaving square holes in the walls. As of 2007, Castle Guedelon is about a third complete.

Once a castle was completed, it was ready for defense. Let's look at medieval siege techniques and the strategies used by both sides.

Medieval Sieges

The Alhambra in Granada, Spain
Karl Weatherly/Photodisc/Getty Images

What happens when an invading army entered a territory and laid siege to its castle? Let's look at siege methods and how the castle's defenders could counter it.

Surround and starve

The invading army surrounded the castle and cut off its supplies of food and water with the hope of starving the defenders. In an effort to spread disease among the defenders, the invaders could use their catapults to send dead or diseased animal and human bodies over the castle walls. They could also loft fiery projectiles to wreak havoc inside the castle. This siege method was actually preferred because the invading army might negotiate the castle's surrender with minimal casualties. But it took months to years to work, and the invading army had to be very well supplied with food and water for the duration of the siege.


If they had time to prepare, the defenders could outlast the siege. They usually brought supplies and people from the surrounding countryside into the castle. Most castles had their own water supplies for this situation. Also, the defenders would usually burn the surrounding countryside so the invading army could not forage it for supplies. Often, the outcome of the siege depended upon whether the invading army or the defending army received reinforcements first.

Scale the walls

The invaders would set huge scaling ladders against the castle's outer curtain wall. Invading soldiers would climb the ladders to gain access to the castle. However, the climbers were vulnerable to arrow fire and objects thrown at them from the battlements on the castle walls. Defenders could also push the ladders off the walls.

Alternatively, the invaders built large wooden siege towers and filled them with soldiers. Other soldiers would wheel the towers to the base of the curtain wall. Soldiers in the top of the tower would lower a plank, storm across it onto the battlements and hope to outnumber the defenders. Siege towers provided cover for the invading soldiers, but they were large and heavy. The invaders were vulnerable as they stormed across the plank single-file. Also, the defenders could set the wooden towers ablaze with flaming arrows.

Ram the doors

If an invading army could break down the castle gate, they could enter the castle relatively easily.So they'd use battering rams (large wooden logs) to pound against the gate (or sometimes the castle walls) and eventually break it. Some battering rams were covered to shield the invading soldiers from the defenders' arrow fire and thrown objects. Sometimes, the wooden castle gates were set on fire to weaken them.

To defend against battering rams, defenders would fire arrows (sometimes flaming). They would often lower soft, padded curtains or wooden walls to lessen the impact of the battering rams. Finally, they could brace the castle doors or gates to withstand the forces of the blows.

And as we mentioned, castle gates had murder holes and arrow loops to help pick off invaders who breached the gate.

Bring down the walls

If an invading army could create a breach in a wall, they could enter the castle in a less defended place. Invaders smashed the walls with battering rams and launched heavy stone projectiles and flaming projectiles at and over the walls. They used catapults, trebuchets (heavy sling weapons) and ballistae (large mounted crossbows).

Another way to bring down castle walls was to mine under them. The invading army would dig tunnels under the castle walls and brace them with timber supports. Once they dug the tunnel far enough to the other side, they would set the tunnel on fire. The timber supports would be destroyed, and the wall above the tunnel would collapse. But defenders could counter by digging under the invading army's tunnel before it reached the wall.

Sieges usually combined all of these tactics. They were expensive, exhausting and time-consuming, but were often necessary to take control of a castle and its territory.

The Decline of Castles

Windsor Castle is an official home of Queen Elizabeth II.
Julian Herbert/Getty Images

After the 16th century, castles declined as a mode of defense, mostly because of the invention and improvement of heavy cannons and mortars. This artillery could throw heavy cannonballs with so much force that even strong curtain walls could not hold up.

Eventually, the medieval castle gave way to fortified cities (almost a reversal of history) and forts (like those seen in Colonial times in North America). Instead of high brick or stone walls, these forts had broad earthen ramparts with wooden or stone palisades on top. The idea was that thick layers of dirt would absorb the impact of cannon fire. Also, these fortifications were easier and faster to build than castles. During the American Revolution at the Battles of Bunker Hill and Dorchester in Boston, the American army fortified their positions almost overnight.


Castles Today

In their heyday, castles were found throughout Europe and the Middle East. Most were in Europe -- there were 10,000 in Germany alone. Although improvements in military technology and the expense of castle construction brought the age of castles to an end, some were built so well that they survive to this day. Some castles are merely ruins, while others have been restored. Surviving castles have been used for many purposes:

  • Some castles, like Windsor Castle, were restored during the 18th and 19th centuries and serve as homes for wealthy or noble families.
  • Historical sites and museums, like the Tower of London, Warwich Castle and Bodiam Castle in England, educate and entertain the public about the Middle Ages.
  • Some castles have been converted into hotels, like Thornbury Castle in England and La Rocca di Monteggiori in Italy.

A number of wealthy industrialists in the 20th century built homes that were designed like castles. Although many of these homes are designed more like palaces than true castles, they are architecturally magnificent and visited by many tourists each year.

  • Publisher William Randolph Hearst built Hearst Castle in California.
  • Hotel magnate George Boldt built Boldt Castle on the St. Lawrence River in upstate New York.
  • Toronto industrialist Sir Henry Mill Pallatt built Casa Loma in Ontario.

For more information about castles, check out the links on the next page.

Lots More Information

Related HowStuffWorks Articles

More Great Links

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  • Castles of the Middle Ages.
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  • Gibson, J, "Anatomy of the Castle", MetroBooks, 2001
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  • Himeji City, Japan, "Himeji Castle." english/himeji/node49.html#SECTION00091000000000000000
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  • Macaulay, D, "Castle", Houghton Mifflin Company, 1977
  • Morris, Marc. "Castle," Channel 4.
  • NOVA Online, "Medieval Siege."
  • Project Guedelon - Google translation of the original French site.
  • Warwick Castle.
  • Yahoo News, "French craftsman build medieval castle." france_building_a_castle