How were castles built in the Middle Ages? The parts of a castle, the builders and the timeline

Architecture · 4 September 2026

Medieval castles were built by lords and kings as fortified homes, in three stages over four centuries: first, from the 10th century, mounds of earth topped with timber towers and ringed by palisades, which a few dozen men could raise in weeks; then, from about 1070, stone keeps and walls that took years and a master mason; and from about 1200, concentric fortresses with two or three rings of wall, round towers and gatehouses stronger than the keep, which were the most expensive buildings of their age. A castle was built where it could control a river crossing, a road or a town, on the highest ground available, with the quarry as close as possible; its plan was a set of obstacles, each covered by the next. Below: the three stages, every part of a castle and what it was for, the builders and the costs, how castles were raised on mountains, and why gunpowder ended them. The stone castles named are in the Buildings by style collection.

Stage 1. Motte and bailey, 950–1150

The first castles were earthworks. A motte was an artificial mound, typically 30 to 60 feet (10–20 m) high, built by digging a ring ditch and piling the spoil in layers with the timber tower on top; a bailey was a lower enclosed yard beside it for the hall, stables and stores, ringed by a ditch, a bank and a wooden palisade. William the Conqueror's army raised them across England after 1066, hundreds of them within a generation, and the Bayeux Tapestry shows one being dug. A motte could be built in weeks by labourers with spades and baskets; the chronicle of Louis of Orléans describes castles of "ditch, bank and stockade" thrown up in eight days. Timber rots and burns, so almost none survive above ground, but the mounds are everywhere in England, Normandy and Ireland.

Stage 2. The stone keep, 1070–1200

Stone came first to the tower. The White Tower of the Tower of London, begun about 1078 by William the Conqueror with a Norman bishop, Gundulf, as architect, is the model: a square block 90 feet (27 m) high with walls up to 15 feet (4.6 m) thick, the entrance on the first floor reached by a removable stair, a well, a chapel, a hall and chambers stacked on three floors, and corner turrets. Keeps like it went up at Rochester, Colchester, Dover and Falaise; in France the donjon of Loches is earlier still. A keep was a last refuge and a statement; the daily life of the castle went on in the bailey around it, which now got a stone curtain wall with towers at intervals. Building a keep took a decade: Dover's, the most expensive in England, cost Henry II about £6,000 in the 1180s, roughly a third of his annual income.

Stage 3. The concentric castle, 1200–1350

The Crusaders came back from the East with the lessons of Byzantine and Muslim fortification, and Edward I of England applied them in Wales in the 1280s: no keep at all, but two complete rings of wall, the inner higher than the outer so archers on both could shoot at once, round towers that had no corners to undermine and gave a field of fire in every direction, and a gatehouse with two towers, a portcullis, murder holes and a drawbridge that was the strongest point of the whole. Beaumaris, Harlech, Conwy and Caernarfon were designed by James of St George, a master from Savoy, and built in five to ten years each with 3,000 workers brought from all over England; Krak des Chevaliers in Syria and Carcassonne in France are the same idea. Concentric castles were the last word in defence and the last generation of castle-building for war.

The parts of a castle

• Moat. A ditch around the walls, dry or filled with water, to stop miners tunnelling under the wall and siege towers being wheeled up to it; the spoil made the banks.
• Curtain wall. The outer wall, 6 to 20 feet thick, with a walkway on top behind the battlements: merlons (the solid parts) and crenels (the gaps) for archers.
• Towers. Set along the curtain wall to project beyond it so archers could shoot along the wall's face; square in the 12th century, round or D-shaped later.
• Gatehouse. The entrance and the strongest building: two towers flanking a passage closed by a drawbridge, one or more portcullises (iron-shod grilles dropped from above), heavy doors, and murder holes in the ceiling for dropping stones or water on attackers who had set fire to the doors. The barbican was an outer gate in front of it.
• Keep, or donjon. The great tower, the lord's residence and final refuge, with its own well and stores.
• Bailey, or ward. The courtyard inside the walls, holding the great hall, kitchen, chapel, stables, smithy, granary and barracks; a concentric castle has an inner and an outer ward.
• Arrow slits. Narrow vertical openings, splayed wide inside so an archer could swing his bow, later with a cross-slit for crossbows.
• Machicolations. Stone projections at the top of a wall with holes in the floor, replacing timber hoardings, to drop things on anyone at the base.
• Well and cistern. No castle could hold out without water; wells were dug through the rock, at Dover to 350 feet.
• Postern, or sally port. A small hidden gate for messengers and sorties.

Who built them, and what it cost

The lord paid and the king licensed: in England a "licence to crenellate" was needed to fortify a house, which is why the records survive. A master mason designed the castle and ran the site, as for a cathedral; under him carpenters for scaffolds, floors and roofs, smiths for tools and ironwork, diggers, quarrymen, carters and lime-burners. Edward I's Welsh castles employed up to 3,000 men at a time, drafted from every county, and cost about £80,000 in total, more than the crown's annual revenue; Beaumaris alone consumed £14,500 and was never finished. A great castle was built in five to fifteen years; a small one in two or three. The stone was quarried as near as possible, often from the moat itself; lime for mortar was burned on site; timber came from the lord's forests. The methods, treadwheel cranes, timber centering for arches and vaults, scaffolding fixed in putlog holes, are the ones described in how cathedrals were built.

Castles on mountains

A castle on a crag was harder to build and harder to take. Builders used the rock as foundation and quarry at once, cutting a level platform and using the stone for the walls, so the castle seems to grow out of the mountain; walls follow the edge of the cliff and towers stand where the approach is easiest. Materials went up by ox-cart on a zigzag road, then by crane or on the backs of men and mules; water was the main problem, solved by cisterns filled from the roofs. Examples: the castles of the Rhine gorge, Hohenzollern, Eltz, Montségur in the Pyrenees, Krak des Chevaliers on its ridge, and the Japanese castles whose stone bases were built on hills in the same century. The Sacred Sanctuary of Castel Sant'Angelo in Rome shows the other route to a castle: a Roman mausoleum walled and towered by the popes.

Why castles ended

Gunpowder. From the 1450s cannon could bring down a high stone wall in days, as the French did to the English castles of Normandy and the Turks to the walls of Constantinople in 1453. High walls became targets rather than protection, and fortification went low and thick: earth ramparts, angled bastions and star forts, the trace italienne of the 16th century, which are not castles. At the same time the nobility wanted comfort: windows, fireplaces, gardens. The result is the château, a palace that keeps the towers and moat as ornament, such as Chambord and Chenonceau on the Loire, or the Renaissance courtyard inside the medieval walls of Wawel in Kraków. The 19th century built castles again as romance: Neuschwanstein in Bavaria, and in the United States the castles of the Hudson valley and Hearst's San Simeon, none of them meant to be attacked. The styles around them are in Romanesque architecture and Gothic architecture.

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