rib vault, inbuilding construction, a skeleton of arches or ribs on which masonry can be laid to form aceiling orroof. Rib vaults were frequently used inmedieval buildings, most famously inGothic cathedrals. Similarly to groin vaults, rib vaults are constructed from two, sometimes three, intersecting vaults, which can be of different widths but must be of the same height. The medieval mason used pointed arches—probably adopted fromIslamic architecture in Spain. Unlike the round arches used inRomanesque cathedrals, pointed arches could be raised as high over a short span as over a long one. The arches are located at the joints of the vaults and carry the weight of the ceiling.

The ribvault arose out of medieval masons’ efforts to solve the challenges associated with supporting heavy masonry ceiling vaults over wide spans. The problem was that the heavy stonework of the traditional archedbarrel vault and the groinvault exerted a tremendous downward and outward pressure that tended to push the walls upon which the vault rested outward, thus collapsing them. Abuilding’s vertical supporting walls thus had to be made extremely thick and heavy in order to contain the barrel vault’s outward thrust. Consequently, windows were few and small in Romanesque churches, and interiors were dark and heavy. Medieval masons solved the problem about 1120 with a number of brilliant innovations—first and foremost, the rib vault. The arching and intersecting stone ribs support a vaulted ceiling surface that is composed of mere thin stone panels. This greatly reduced the weight (and thus the outward thrust) of the ceiling vault, and, since the vault’s weight was now carried at discrete points (the ribs) rather than along a continuous wall edge, separate widely spaced vertical piers to support the ribs could replace the continuous thick walls. The round arches of the barrel vault were replaced by pointed (Gothic) arches, which distributed thrust in more directions downward from the topmost point of thearch.

Decades of experimentation produced vaulting that was light, strong, open, versatile, and applicable everywhere. Combined with such otherinnovations asflying buttresses, rib vaults allowed Gothic buildings to become, in succession, broader and taller. How their visual appearance changed is easy to see if one compares, for instance, the tall and airy 13th-centuryReims Cathedral inFrance with the stout 11th-centuryDurham Cathedral in England.