Collier's New Encyclopedia (1921)/Donjon

DONJON, the grand central tower of a Norman or mediæval castle, frequently raised on an artificial elevation. It was the strongest portion of the building, a high square tower with walls of enormous thickness, usually detached from the surrounding buildings by an open space walled, called the Inner Bailey, and another beyond called the Outer Bailey. Here, in case of the outward defenses being gained, the garrison retreated to make their last stand. The donjon contained the great hall, and principal rooms of state for solemn occasions, and also the prison fortress; from which last circumstance we derive the modern and restricted use of the word dungeon. Examples are seen in the White Tower, in the Tower of London, Rochester Castle, and in the Castle at Newcastle. It was also called the donjon-keep.