turret

In architecture, a turret (from Italian: torretta, little tower; Latin: turris, tower) is a small tower that projects vertically from the wall of a building such as a medieval castle. Turrets were used to provide a projecting defensive position allowing covering fire to the adjacent wall in the days of military fortification. As their military use faded, turrets were used for decorative purposes, as in the Scottish baronial style.
A turret can have a circular top with crenellations as seen in the picture at right, a pointed roof, or other kind of apex. It might contain a staircase if it projects higher than the building; however, a turret is not necessarily higher than the rest of the building; in this case, it is typically part of a room, that can be simply walked into – see the turret of Chateau de Chaumont on the collection of turrets, which also illustrates a turret on a modern skyscraper.
A building may have both towers and turrets; turrets might be smaller or higher but the difference is generally considered to be that a turret projects from the edge of the building, rather than continuing to the ground. The size of a turret is therefore limited by technology, since it puts additional stresses on the structure of the building. It would traditionally be supported by a corbel.

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