Medieval Castles: How They Were Built, Defended and Attacked

Medieval castles were fortresses, residences, administrative centers and symbols of political power. Their towers and walls dominate the modern image of the Middle Ages, but castles changed dramatically over time.

Early castles could be built rapidly from earth and timber. Later fortifications used massive stone keeps, curtain walls, towers, fortified gatehouses and multiple defensive lines. Attackers responded with siege towers, battering rams, trebuchets, mining and eventually gunpowder artillery.

A castle was therefore never simply a stone building. It was part military base, part noble household and part statement of authority over the surrounding landscape.

For the wider period, start with our Middle Ages overview or explore the Medieval History hub.

What is a medieval castle?

A medieval castle was a fortified residence associated with a king, lord or other powerful authority.

Unlike a simple defensive wall or temporary military camp, a castle usually combined military protection with residential and administrative functions.

Castles could protect strategic roads, river crossings, ports and borders. They could also house officials, store supplies, collect taxes and demonstrate control over newly conquered territory.

Why were castles built?

Castles were built for several overlapping reasons:

• to defend territory;
• to control roads, rivers and towns;
• to protect rulers and noble households;
• to store weapons and supplies;
• to serve as administrative centers;
• to intimidate rivals and local populations;
• to display wealth, prestige and political authority.

English Heritage emphasizes that medieval castles were both defensive structures and elite residences. Their architecture communicated status as well as military strength.

When were medieval castles first built?

Fortified elite residences existed before the Middle Ages, but the castle as a characteristic institution of medieval western Europe developed especially from the ninth and tenth centuries onward.

In England, castle building expanded dramatically after the Norman Conquest of 1066.

William the Conqueror and his followers used castles to secure territory, control settlements and suppress resistance.

Norman castles after 1066

After defeating Harold II at the Battle of Hastings, William needed to control a kingdom where Norman forces were a relatively small ruling minority.

Castles offered a practical solution.

English Heritage records that more than 500 castles were raised in England during the first twenty years after 1066.

Many were fast earth-and-timber fortifications rather than the huge stone castles tourists see today.

What was a motte-and-bailey castle?

The motte-and-bailey became one of the best-known early castle forms.

The motte was an artificial or adapted mound topped by a fortified tower or strongpoint.

The bailey was an enclosed courtyard protected by a ditch, bank and wooden palisade.

The bailey contained the working buildings of the castle, which could include halls, kitchens, workshops, stables, stores and accommodation.

Why were motte-and-bailey castles useful?

They could be built more quickly than large stone fortresses.

Earth, timber and local labor were readily available.

The raised motte provided a strong defensive position and a commanding view over the surrounding area.

For conquerors trying to control new territory rapidly, speed mattered enormously.

Were wooden castles weak?

Wooden defenses were vulnerable to fire and decay, but that does not mean they were militarily useless.

A steep mound, ditch, earth bank and timber palisade could create a substantial obstacle.

Many early castles remained effective for years before their defenses were upgraded or replaced in stone.

Why did castles become stone?

Stone was more durable and resistant to fire than timber.

It also allowed rulers to construct larger and more permanent buildings.

Replacing timber with stone was expensive, so conversion often happened gradually.

A wooden palisade might become a stone curtain wall while other buildings remained timber.

The stone keep

The keep, also called the great tower or donjon, became the most imposing building in many early stone castles.

It could serve as a strongpoint, residence, storage space and symbol of lordship.

The White Tower at the Tower of London is one of the most famous examples of a Norman great tower.

What was inside a castle keep?

Large keeps could contain:

• a great hall;
• private chambers;
• a chapel;
• storage rooms;
• latrines;
• fireplaces;
• guard rooms;
• sometimes wells or cisterns.

Not every keep had the same layout, and some were used more as defensive or ceremonial buildings than comfortable permanent homes.

Why did keep designs change?

Large rectangular keeps looked powerful, but their corners could be vulnerable to attack and undermining.

At Rochester Castle in 1215, attackers mined beneath a corner of the keep and brought part of it down.

From the late twelfth century, castle builders increasingly experimented with round, polygonal and cylindrical towers, which could be harder to undermine and offered fewer exposed corners.

What was a curtain wall?

A curtain wall was the defensive wall surrounding a castle’s courtyard or ward.

Stone curtain walls could be very thick and high.

They were often strengthened with towers that projected outward, allowing defenders to shoot along the face of the wall as well as directly outward.

Why were towers built into castle walls?

A projecting tower gave defenders a better angle of fire against attackers approaching the wall.

Round or D-shaped towers also reduced vulnerable sharp corners.

Towers could contain guard rooms, storage, accommodation and firing positions.

Battlements and crenellations

The top of a defensive wall often had a protected walkway.

Battlements consisted of alternating raised sections and gaps.

The raised parts are called merlons; the openings are crenels or embrasures.

Defenders could use the openings to shoot while taking cover behind the stonework.

Arrow slits

Narrow openings in walls allowed archers or crossbowmen to fire while exposing only a small part of the body.

These openings are commonly called arrow slits or loops.

Their shape varied depending on period, weapon and architectural design.

The castle gatehouse

The entrance was often one of the weakest points in a fortress, so castle builders developed increasingly elaborate gatehouses.

By the later Middle Ages, a gatehouse could be one of the strongest buildings in the entire castle.

Large gatehouses often combined military defenses with impressive residential rooms above the entrance.

How was a castle gate defended?

Possible defensive features included:

• drawbridges;
• portcullises;
• heavy wooden doors;
• guard chambers;
• arrow loops;
• multiple gateways;
• defensive towers.

An attacker who broke through one barrier might still find another obstacle immediately behind it.

What was a portcullis?

A portcullis was a heavy vertical grille, often made of timber reinforced with iron.

It could be raised or dropped through grooves inside a gateway.

Some elaborate gatehouses had more than one portcullis.

Did castles really pour boiling oil on attackers?

The image of defenders constantly pouring boiling oil from walls is exaggerated.

Oil was expensive and had many other uses.

Defenders could drop stones or use other materials and weapons against attackers below.

Some later fortifications included openings that allowed defenders to attack enemies immediately beneath walls or gates, but the popular boiling-oil stereotype should not be treated as standard castle practice.

What were machicolations?

Machicolations were projecting stone defenses with openings in the floor.

They allowed defenders to attack enemies directly below parts of a wall or gate.

They were more common in some regions and periods than others and became an important visual feature of later medieval fortification.

What was a moat?

A moat was a defensive ditch surrounding part or all of a castle.

Some moats contained water, while others were dry.

Moats made it harder for attackers to reach walls, use siege towers or undermine foundations.

A wide ditch could be as important defensively as a high wall.

Did every castle have a water-filled moat?

No.

Many castles had dry ditches.

Whether a moat held water depended on geography, engineering and the design of the site.

What was a concentric castle?

A concentric castle used multiple defensive circuits so that one line of walls supported another.

Attackers who captured the outer defenses still faced an inner wall.

By about 1250, Dover Castle had developed inner and outer circuits of towered walls.

English Heritage describes Dover as the first concentric fortress in western Europe.

Edward I’s castles in Wales

Some of the most famous examples of sophisticated late-thirteenth-century castle building are associated with Edward I’s conquest of north Wales.

Castles such as Beaumaris, Harlech, Conwy and Caernarfon combined powerful walls, towers and gatehouses.

These structures were not neutral pieces of architecture. They were part of a military and political program designed to control conquered territory.

How were castles built?

Castle construction required enormous quantities of labor and material.

A major stone castle might involve:

• masons;
• carpenters;
• quarry workers;
• blacksmiths;
• laborers;
• cart drivers;
• engineers;
• administrators responsible for wages and supplies.

Stone had to be quarried, shaped and transported. Timber was needed for roofs, floors, doors, scaffolding and temporary construction equipment.

How long did it take to build a castle?

There was no standard construction time.

A simple earth-and-timber castle might be created quickly, while a major stone fortress could develop over many years or even generations.

Castles were constantly repaired and remodeled as military technology, wealth and fashion changed.

How much did castles cost?

Large royal castles were extremely expensive.

The costs included not only stone and labor but also transport, food, timber, metalwork, specialist craftsmen and permanent garrisons.

Major castle-building programs were therefore demonstrations of economic power as well as engineering skill.

What was daily life in a castle like?

A castle could be crowded with far more than soldiers.

Residents might include:

• the lord and family;
• knights and guards;
• clerks and administrators;
• cooks;
• servants;
• craft workers;
• stable staff;
• chaplains;
• visiting nobles and messengers.

When a king or major noble arrived with a household, the population could increase dramatically.

The great hall

The great hall was a central social and administrative space.

Meals, ceremonies, meetings and legal business could take place there.

Seating arrangements reflected social hierarchy.

The hall was not simply a dining room; it was a public stage for lordship.

Where did people sleep?

Elite residents might have private chambers, especially in later castles.

Lower-status servants and soldiers had much less privacy.

Sleeping arrangements depended on status, the size of the castle and whether it was occupied permanently or temporarily.

How were castles heated?

Early rooms could be cold and difficult to heat.

Fireplaces became increasingly common in elite residential spaces.

Wall hangings, wooden paneling and enclosed chambers also helped make interiors more comfortable.

Stone castles were not uniformly freezing, but maintaining warmth in large rooms could require substantial fuel.

Castle toilets

Medieval castles had latrines, often called garderobes.

Waste might fall through shafts to pits, ditches or the outside of a wall.

Designs varied greatly, and sanitation by modern standards remained limited.

Where did castles get water?

Water supply was crucial, especially during a siege.

Castles could use wells, cisterns, springs or stored water.

A fortress without secure access to water was extremely vulnerable if surrounded.

How were castles attacked?

Storming a strong castle directly could be extremely costly.

Attackers therefore used multiple strategies:

• blockade and starvation;
• bombardment;
• battering rams;
• ladders;
• siege towers;
• mining under walls;
• negotiation and bribery;
• surprise attack or treachery.

Many sieges were contests of logistics rather than dramatic assaults.

Why starve a castle instead of storming it?

If a garrison had limited food and water, attackers could simply surround it and wait.

This avoided the enormous casualties of attacking walls directly.

The defenders, however, hoped that disease, cost, bad weather or a relieving army would force the besiegers to leave first.

Siege warfare was therefore often a race between two supply systems.

The trebuchet

The trebuchet was one of the most famous medieval siege engines.

Large counterweight trebuchets could throw heavy stones against walls or into a castle interior.

Smaller traction trebuchets used teams pulling ropes to power the throwing arm.

English Heritage notes that the first recorded use of a trebuchet in England occurred during the siege of Dover Castle in 1216.

Did trebuchets destroy castle walls easily?

Not always.

Well-built stone walls could withstand repeated bombardment.

Missiles could damage battlements, roofs and buildings and exert enormous psychological pressure on a garrison.

But attackers often needed other methods to create a usable breach.

Battering rams

Battering rams were designed to strike gates or masonry repeatedly.

Attackers could protect the crews under a timber shelter.

Defenders tried to burn, break or attack the ram and its operators.

Siege towers

Wooden siege towers could bring attackers close to the height of castle walls.

Archers or crossbowmen could shoot from upper levels while troops attempted to cross onto the battlements.

They required suitable terrain and were vulnerable to fire.

Mining under castle walls

Mining was one of the most dangerous siege techniques.

Attackers dug a tunnel beneath a wall or tower foundation.

The excavated space could be temporarily supported by timber props.

When the props were burned or removed, part of the structure above could collapse.

The siege of Rochester Castle in 1215

Rochester provides a famous example of medieval mining.

King John’s forces besieged rebels holding the castle in 1215.

Miners attacked the south-east corner of the great keep.

English Heritage records that the attackers used the fat from pigs as fuel to burn the timber supports in the mine, helping bring down part of the tower.

The defenders still resisted inside the remaining portion of the keep until starvation forced surrender.

Countermining

Defenders could sometimes dig their own tunnels to intercept attackers’ mines.

Listening for underground digging could provide warning.

Underground fighting was dangerous because tunnels could collapse and visibility was extremely poor.

Scaling ladders

Attackers could try to climb walls with ladders in a direct assault known as escalade.

This was fast but extremely dangerous.

Soldiers were exposed to arrows, crossbow bolts, stones and close-range attack from defenders above.

How many soldiers defended a castle?

Garrison size varied enormously.

A castle in peacetime might contain relatively few soldiers, while an important fortress expecting attack could hold a much larger force.

A small group behind strong defenses could sometimes resist an army far larger than itself.

This ability to multiply defensive strength was one of the main military advantages of castles.

Could castles be captured without fighting?

Yes.

Negotiation, betrayal, political surrender and bribery could be more effective than military assault.

Sieges were expensive for both sides, so negotiated surrender was common.

Defenders might agree to yield after a set period if no relief army arrived.

What happened when a castle surrendered?

Terms varied.

A garrison that surrendered early might be allowed to leave safely.

Defenders who resisted until a fortress was stormed could face far harsher treatment.

Much depended on politics, custom and the anger of the victorious army.

Castles as symbols of power

Military usefulness was only one reason to build a castle.

A huge keep or gatehouse could dominate the landscape and visually communicate who controlled the region.

Royal and aristocratic castles also hosted feasts, courts, diplomacy and ceremonies.

Architecture was political theater.

Were castles comfortable homes?

Some were.

Large later medieval castles could contain private apartments, glazed windows, fireplaces, chapels and decorated halls.

Elite residence became increasingly important as military design evolved.

But comfort varied greatly, and an active military fortress could remain noisy, crowded and inconvenient.

Castle kitchens

Major households needed large quantities of food.

Castle kitchens could contain ovens, hearths, preparation tables and storage areas.

Feeding a noble household, visitors and a garrison required complex supply arrangements.

During a siege, food storage became a matter of survival.

Castle chapels

Religion was part of everyday elite life.

Many castles contained chapels where residents attended services.

Royal and noble castles might employ permanent chaplains.

Castle prisons

Some castles held prisoners, especially high-status political captives.

But the popular idea that every castle possessed vast underground dungeons is exaggerated.

Prisoners could be held in towers, chambers or other secure rooms.

Why did castles decline?

Castles did not suddenly become useless at the end of the Middle Ages.

Some continued as residences, administrative centers and military bases for centuries.

But several changes reduced the importance of the traditional high-walled medieval fortress.

Gunpowder artillery

Gunpowder weapons appeared in European warfare during the later Middle Ages.

As cannon became larger and more effective, tall vertical stone walls became increasingly vulnerable.

Fortification design gradually shifted toward lower, thicker defenses better able to resist artillery.

The change took centuries rather than happening immediately.

From castles to palaces and artillery forts

As political states became more centralized, many nobles had less need for independent private fortresses.

Elite architecture increasingly emphasized comfortable palaces and country houses.

Where serious military fortification remained necessary, engineers developed new forms specifically designed for cannon warfare.

Did castles stop being used after the Middle Ages?

No.

Many medieval castles were reused during later conflicts.

Some were strengthened for artillery. Others became military barracks, prisons or residences.

Several medieval castles were besieged again during the English Civil War in the seventeenth century.

See our guide to the English Civil War for the later transformation of warfare and fortified strongholds.

Famous medieval castles

Some of the best-known surviving examples illustrate different stages of castle development:

• Tower of London: Norman great tower and later royal fortress.
• Windsor Castle: royal castle developed continuously across centuries.
• Dover Castle: major keep surrounded by increasingly sophisticated defensive lines.
• Rochester Castle: famous Norman keep and siege of 1215.
• Conwy Castle: part of Edward I’s Welsh castle program.
• Caernarfon Castle: monumental royal fortress in north Wales.
• Harlech Castle: sophisticated late-thirteenth-century fortress.
• Beaumaris Castle: celebrated for its concentric defensive planning.

Medieval castle timeline

• 9th–10th centuries: fortified aristocratic residences expand in parts of western Europe.
• 1066 onward: Norman castle building spreads rapidly across England.
• 11th–12th centuries: many timber defenses are rebuilt in stone.
• 12th century: large stone keeps become major symbols of royal and noble power.
• late 12th–13th centuries: greater use of round towers, strengthened gatehouses and curtain walls.
• 13th century: concentric principles reach a high level of sophistication.
• 1277–1294: Edward I builds major castles during the conquest of north Wales.
• 14th century: gunpowder weapons begin appearing in European siege warfare.
• 15th–16th centuries: artillery increasingly changes fortress design.

Medieval castle myths

Myth: every castle was made of stone

Many early castles were built primarily from earth and timber.

Myth: every castle had a moat full of water

Many defensive ditches were dry.

Myth: defenders constantly poured boiling oil

Boiling oil is heavily emphasized in popular culture but was not a routine universal castle defense.

Myth: the keep was always where everyone lived

Castle households could occupy halls and chambers elsewhere in the bailey or ward. The role of the keep differed between castles.

Myth: castles became useless the moment cannon appeared

The transition took a long time. Medieval castles continued to be adapted and used long after gunpowder weapons appeared.

Medieval castles FAQ

What was the strongest part of a medieval castle?

It depended on the design. In early castles the keep could be the principal strongpoint, while later castles often concentrated enormous defensive strength in gatehouses, towered curtain walls and multiple defensive circuits.

Why were castle walls so thick?

Thick masonry resisted impact, fire and attempts to breach or undermine the wall. Thickness also allowed protected walkways and defensive spaces.

What is the difference between a castle and a palace?

A castle is fundamentally a fortified residence, while a palace emphasizes elite residence and ceremony without necessarily being designed for serious military defense.

What is a motte?

A motte is the raised mound of a motte-and-bailey castle, usually topped by a fortified structure.

What is a bailey?

The bailey is the enclosed courtyard containing many of the castle’s domestic, military and service buildings.

How were castles captured?

Attackers could use starvation, bombardment, mining, ladders, battering rams, siege towers, negotiation or betrayal.

Why did castles stop being built?

They did not simply stop. Traditional castle architecture gradually gave way to artillery fortifications and more comfortable elite residences as warfare and political organization changed.

Sources and further reading

• English Heritage — Medieval Castles
• English Heritage — Castles Through Time
• English Heritage — Medieval Warfare and Castle Development
• English Heritage — Medieval Siege Warfare
• John Goodall, The English Castle 1066–1650.
• R. Allen Brown, English Castles.