The Columbia Encyclopedia, Sixth Edition. 2001-07.
clerestory
or clearstory (both: klr´str´´, –stôr´´) (KEY) , a part of a building whose walls rise higher than the roofs of adjoining parts of the structure. Pierced by windows, it is chiefly a device for obtaining extra light. It had an early use in certain Egyptian temples, as at Karnak, and was used later in the great halls of Roman basilicas. It became a characteristic element of medieval churches, receiving its fullest development in churches of the Gothic period.
r´st
r´´
, –stôr´´
