Bailey, Keep, and Curtain Wall Explained
A first visit to a major medieval castle can be bewildering. Guides use architectural terms that assume prior knowledge; information boards describe features in relation to other features that the visitor has not yet located. This guide works through the fundamental vocabulary of castle architecture — bailey, keep, curtain wall, gatehouse, barbican, and the rest — in the order you would encounter them moving from outside to inside a fully developed medieval castle. The map shows every type described here across thousands of surviving sites.
Motte and Bailey: The Starting Point
The earliest castle form familiar in northern European archaeology is the motte-and-bailey. The motte is an earthen mound — either natural or artificially raised — surmounted by a timber tower or palisade. The bailey is the enclosed courtyard at the base of the motte, protected by its own ditch and palisade. The bailey contained the domestic buildings: hall, kitchen, stables, and well. The motte was the last-resort position if the bailey was overrun.
Motte-and-bailey castles could be constructed in days or weeks with unskilled labour. The Normans built them across England after 1066 at extraordinary speed — over 500 have been identified archaeologically. They were effective but impermanent: the timber decayed, the earth compacted and slumped, and the height of the motte limited the weight of any superstructure. The 12th century saw the gradual replacement of timber with stone, beginning with the most strategically important sites.
The Keep
The keep — in French, the donjon, from which the word dungeon derives — is the primary tower of a stone castle: the building that served simultaneously as the lord's residence, the garrison's strongpoint, and the symbol of authority. In English 12th-century castle building, the standard form is the great square keep: a massive rectangular tower of two or three storeys, with walls typically 3-5 metres thick, a single entrance at first-floor level (reached by an external stair that could be removed), and few windows in the lower storeys.
The Tower of London's White Tower, begun by William the Conqueror in the 1070s and substantially complete by 1100, is the defining example. Its walls are 4.6 metres thick at the base; the entrance was originally at first-floor level on the south side. Dover Castle's inner keep, built for Henry II from 1180-85, is the developed form: more regularly planned, with flanking towers, and more domestic in its upper floors.
The Curtain Wall
The curtain wall is the perimeter wall of a castle or fortified enclosure. The term distinguishes it from a city wall (which encloses an urban area) and from the keep (which is a free-standing tower). A simple enclosure castle — a bailey with a stone wall replacing the timber palisade — may have nothing more than a curtain wall and a single tower; the domestic buildings stand against the inner face of the wall.
The height and thickness of curtain walls increased through the 12th and 13th centuries as trebuchet technology improved and the threat of mining became better understood. By the late 13th century, Edward I's Welsh castle-building programme — Caernarfon, Harlech, Beaumaris, Conwy — produced curtain walls of 3-4 metres thickness and 10-12 metres height, with mural towers projecting at intervals to allow flanking fire along the wall face.
Flanking Towers
The mural tower — a tower projecting from or through the curtain wall — is the most important development in castle design between the Norman period and the 14th century. A plain curtain wall, however high, has a fatal weakness: the base of the wall face is in dead ground, invisible from the wall-top. Attackers can press against it to place ladders or mining tools without being directly observed or targeted.
The projecting tower eliminates the dead ground by allowing defenders to fire along the face of the adjacent curtain from the tower's flanking arrow loops. The round tower, which became standard in the 13th century after the square towers of Norman design were shown to be vulnerable to mining at the corners, also deflects projectile impacts more efficiently than a flat face. The round flanking towers of Chateau Gaillard (1196-98), designed by Richard I of England with explicit attention to this lesson, are among the earliest systematic applications of the principle.
The Gatehouse
The gate is the weakest point of any castle perimeter — an opening through which the castle's own occupants must pass, and therefore an opening that cannot be filled with stone. The history of castle design is substantially the history of making that opening as defensible as possible.
The developed medieval gatehouse is a tower block straddling the gate passage, with portcullis grooves, a drawbridge or pit, arrow loops covering the approach, and murder holes — openings in the ceiling of the gate passage through which defenders could pour water (to douse fire), drop missiles, or shoot — in the ceiling above. By the 13th century, twin-towered gatehouses flanking a deep passage were standard at major castles.
The Barbican
A barbican is an outwork protecting the main gate — an additional obstacle placed in front of the gatehouse to delay and expose attackers before they reach the gate itself. Its form varies: it may be a simple walled enclosure through which the approach road passes, a pair of towers flanking the approach, or (in the most developed form) a separate fortified structure with its own gate and portcullis.
The barbican at Lewes Castle in England, built in the early 14th century, is one of the most complete survivors: a twin-towered structure placed in front of the original Norman gate, forcing attackers to fight through a second fortified passage before reaching the main gate.
The Bailey and Its Buildings
The bailey — the courtyard enclosed by the curtain wall — is the functional heart of the castle. In a fully developed medieval castle, the bailey contains the great hall (the principal social and administrative space), the kitchen range (usually built against the wall to reduce fire risk to the main buildings), the chapel, the stabling, the well, and the accommodation for the garrison and household. The lord's private quarters might be in a solar tower or in the upper floors of the keep.
Many castles have two baileys — an outer and an inner — with the inner containing the lord's residence and principal buildings, and the outer containing the more utilitarian structures. Concentric castles such as Beaumaris, designed entirely on paper by Edward I's military engineer James of Saint George, take this to its logical conclusion: two complete rings of fortification, the outer lower than the inner so that defenders on the inner can fire over the outer.
Machicolations and Hoardings
A machicolation is a projecting parapet supported on corbels, with openings in the floor through which defenders can drop objects on attackers at the base of the wall directly below. It is the stone version of the timber hoarding — a projecting wooden gallery fitted to the top of a wall-walk in wartime to create the same effect. Machicolations became standard in French military architecture from the mid-13th century; in English castle building they were less common, hoardings being preferred for their flexibility.
Where will you go first?
Every term described in this guide corresponds to physical features visible at thousands of sites on the interactive map. Filtering by country and region allows you to compare the full development of these forms from early Norman earthworks to late medieval concentric stone fortresses.