A keep is a strong central tower which normally forms the heart of a castle. Often the keep is the most defended area of a castle, and as such may form the main habitation area, or contain important stores such as the armoury or the main well. An earlier word for a keep, still used for some medieval monuments, is donjon.

Although the most common form of a keep was a stone building in the centre of a set of walls, some castles were in fact no more than a keep. Often these are simply referred to as tower houses.

Keeps, or donjons as they are generally referred to in France, come in a remarkable variety of shapes and sizes. They can be of 'square' variety, generally found on the British Isles, cylindrical, octagonal, regular and irregular polygonal forms, or a combination or several of these features.

One unique form is the shell-keep which essentially a masonry 'fossilization' of a palisade lining the top of a castle defensive mound or motte.

Famous keeps

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One of the most famous keeps in Europe is the celebrated White Tower of The Tower of London, constructed by William the Conqueror in the aftermath of the Norman Conquest. Another example is the massive keep of Rochester Castle that still towers over the city today. The cylindrical donjon of Rouen, shown at right, is all that remains of the large city fortress where Joan of Arc was imprisoned during her trial for heresy. The largest keep in existence is the donjon of Château de Vincennes in a suburb of Paris. The title was held previously by the donjon of Coucy in Picardy.

Fortification | Human habitats

Donjon | Donjon | Bergfried | Donjon | Öregtorony | 天守 | Donjon | stołp | Kärntorn