Vault

   An arched ceiling built of brick, stone, or concrete. Of these materials, concrete is the most effective as it allows for greater expanses since it forms one solid, rigid, surface requiring a lesser number of internal supports. The solid surfaces can then be decorated with coffers, mosaics, or frescoes. There are many types of vaults. A barrel vault is a tunnel-like, semicylindrical ceiling, while a groin or cross vault is composed of two intersecting barrel vaults at right angles. The advantage of this system is that it allows for the inclusion of windows on the sides to bring lighting into the interior of the structure it covers. Groin vaults also require less construction materials and labor. Sometimes the groin vaults are ribbed. The ribs serve various purposes: to reduce the number of wooden supports needed during construction, to lighten the thickness of the groin vaults and therefore allowing for larger windows, and to visually separate them into segments, their repetition granting a rhythmic quality to the building. Pointed ribs, common in Gothic architecture, provide greater stability than the rounded ribs of Romanesque construction. A dome is another type of vaulting, a semicircular structure that sits on a drum or is carried by pendentives. Domes are often placed above the crossing (where the nave and transept cross) of churches. Their lantern and piercings on the drum allow for light to radiate over the altar, giving it a mystical quality.