A cruck or crook frame is a curved timber, one of a pair, which supports the roof of a building, used particularly in England. This type of timber framing consists of long, generally bent, timber beams that lean inwards and form the ridge of the roof. These posts are then generally secured by a horizontal beam which then forms an 'A' shape. Crucks were chiefly in use in the medieval period for structures such as large tithe barns.