1911 Encyclopædia Britannica/Keep

KEEP (corresponding to the French donjon), in architecture the inmost and strongest part of a medieval castle, answering to the citadel of modern times. The arrangement is said to have originated with Gundulf, bishop of Rochester (d. 1108), architect of the White Tower. The Norman keep is generally a very massive square tower. There is generally a well in a medieval keep, ingeniously concealed in the thickness of a wall or in a pillar. The most celebrated keeps of Norman times in England are the White Tower in London, those at Rochester Arundel and Newcastle, Castle Hedingham, &c. When the keep was circular, as at Conisborough and Windsor, it was called a “shell-keep” (see Castle). The verb “to keep,” from which the noun with its particular meaning here treated was formed, appears in O.E. as cépan, of which the derivation is unknown; no words related to it are found in cognate languages. The earliest meaning (c. 1000) appears to have been to lay hold of, to seize, from which its common uses of to guard, observe, retain possession of, have developed.