Keep

Part of a castle, a keep was the large tower which the Normans built all over England on the top of their mottes. Generally it was square and made of stone; initially probably only 2 or 3 stories, but as building techniques improved some got to 5 floors high.

As castle-building developed, the keep became, variously, the main tower in a curtain wall, the principal tower of a more complicated castle, or simply the central building where the main "offices" (such as the constable, the steward, the treasurer) were housed.