Castle
Keep

A keep was a great tower or other building that served as the main living quarters of the castle and usually the most strongly defended point of a castle before the introduction of concentric defence. "Keep" was not a term used in the medieval period – the term was applied from the 16th century onwards – instead " donjon " was used to refer to great towers, or turris in Latin. In motte-and-bailey castles, the keep was on top of the motte. "Dungeon" is a corrupted form of "donjon" and means a dark, unwelcoming prison. Although often the strongest part of a castle and a last place of refuge if the outer defences fell, the keep was not left empty in case of attack but was used as a residence by the lord who owned the castle, or his guests or representatives.

At first, this was usual only in England, when after the Norman Conquest of 1066 the "conquerors lived for a long time in a constant state of alert"; elsewhere the lord's wife presided over a separate residence (domus, aula or mansio in Latin) close to the keep, and the donjon was a barracks and headquarters. Gradually, the two functions merged into the same building, and the highest residential storeys had large windows; as a result for many structures, it is difficult to find an appropriate term. The massive internal spaces seen in many surviving donjons can be misleading; they would have been divided into several rooms by light partitions, as in a modern office building. Even in some large castles the great hall was separated only by a partition from the lord's chamber, his bedroom and to some extent his office.
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