VAULT, an arched-covered enclosure, hence frequently used to express the arched ceiling or roof, as of a hall, room, cellar or other compartment or edifice. In a still further extension the term vault is frequently used as synonymous with a subterranean compartment, as a crypt, cellar, etc. In architecture it must be noted that vaults are ceilings not roofs, as those below ground (crypts, etc.) carry the floor above and even in the case of naves and aisles of churches the vaulting may carry a solid masonry roof, as in Milan Cathedral and the Romanesque buildings of southern France. While the art of vault construction dates back to unknown origins and the Romans excelled in the art, it was in the Middle Ages that archi tecture took up seriously the important phase of creating its decoration in the actual con struction itself, and vaulting was the greatest problem of the architect in his construction. The early Christian basilica, from its pagan prototype, had at the far end of its flat roof a half dome or demi-hemisphere (apse). In Romanesque architecture (say 11th century to middle 12th century) the naves and aisles of the church edifices were covered, in sequence, with the following styles of vaults: First the cupola (domical), next the tunnel vault, then the groined vault. Out of the latter developed the ((ribbed? and the Gothic era in vaulting arose.
Various authorities divide vaults into two classes as to their construction: Solid and Ribbed, and, as to form, into Simple and Compound. Solid are those having un broken surfaces whereas the ribbed refer to those with variegated inner surface planes. Simple are those vaults composed of an un changed form of archway throughout. Com pound vaults are those broken up by intersect ing arches. A simple vault is the cylindrical, termed barrel, tunnel, cradle or wagon vault a mere arch extended in its axis to roof over a compartment or other space. The tunnel or barrel is the commonest in use and has usually a semi-circular cross section and the inner or surface° (intrados) has the form of a portion of a hollow cylinder. (Fig. 1). Barrel with spiral axis; used for supporting winding stairs, etc. Still another kind belonging to this category is the expanding vault; these are smaller at one end than the other and the inner surface diminishing has a form of part of a truncated cone or elongated funnel. Such are found in Romanesque style buildings to form pendentives (Fig. 3) to assist in reducing a square to an octagon and may occur as parts of compound vaults. Compound vaults are, as before stated, simple vaults intersecting one another. (Fig. 4). They usually are termed proined vaults on account of the groin angle vaults may, however, have cross sections semi elliptical, segmental, pointed, three centred, etc. Barrel vaults date back at least to 800 a.c. as found in the pyramids at Meroc and at Nim roud. In the case of the aisles of church build which the two surfaces produce at their junc ture. These compound vaults may be divided into: quadripartite (four-part), oblique, irregu lar, etc. The quadripartite form is evolved from two barrel vaults intersecting. (Fig. 4). In covering a square compartment it is the common groin vault; in domical vaults, it is the so-called ((cloistered arch" or square dome, etc. Covering oblong compartments of such we have, among others, the ((Welsh° or ((under pitch" vaults (Fig. 5) with the surface parts cylindrical usually and the groin line becomes a hyperbola. In the square compartmedt also comes the ((stilted' vault composed of cylindri cal vaults but with the transverse narrower ings a "half-barrel° vault is frequently used having a 45 degrees segment of a circle. (Fig.
2). Another simple vault is a skew arch which has been described as °a barrel vault whose ends are in parallel planes oblique to the axis'and whose joints are spirals.* The annular vault also belongs to the simple series. This has its axis curved ; its intrados, therefore, is a por tion of a cylindrical or hollow ring. The spiral vault also belongs here, and is an annular vault than the main and springing from a higher level, causing the groin line to assume a double curve. They are found frequently covering Roman halls and baths and appear in French Romanesque. Oblique vaults can occur with straight axes composed of equal or unequal barrel vaults; with an annular vault intersected by a conical vault, or by an nnderpitch vault. (Fig. 5). Irregular vaults are those in this category which do not conform to any regular geometrical shape. This section is subdivided into tripartite and polygonal, according to whether, in the first case, they cover a triangu lar space caused, for instance, from the inter section of three barrel or three expanding vaults; or, in the polygonal case, whether they Cover octagonal, decagonal, etc., rooms. Fan Tracery vaulting is a solid variety common in the Later Gothic period. It contains no ribs in the construction (see Ribbed Vaulting Gothic), but the surfaces are covered ornamentally with' mullions and tracery bars enclosing panels. Saint George's Chapel, Windsor, England, is a fine example. Fan-tracery vaults can be sub divided into pyramidoidal and conoidal. In the former case two halves of an inverted concave pyramidoid are set opposite each other, their bases forming the ridge of the arch. The con oidal class, as its name implies, is of circular section not having angles as do the pyrami doidal. Pyramidoids and conoids are called sometimes pendentives. (See Fig. 3). In Rib vaulting the surfaces are outlined into panels by a rib structure or raised frame-work. Orig inally the ribbing was first constructed sepa rately, then the panel filled in and supported by the ribs. Frequently in later work the rib bing is a purely ornamental addition. The rib, with the ribbed vault we enter the Gothic era. The dome had for its support pendentives, either the spherical or the squinch° (see Fig. 6) or the °trumpet' arch. While there have been spherical pendentives found in Byzantine architecture it was in the 6th century that this system of vaulting was used first largely. But the squinch is found in Roman architecture early as about 138 A.D. (Villa Adriana at Tivoli). The squinch which is a lintel, corbel or arch built into and projecting from the interior cor ner of two walls, was used in the Byzantine period along with the pendentive to support the dome. The spherical pendentive is found as dome support for the Romanesque period. There are a few naves of Romanesque churches found consisting of domes supported on squinches (Notre Dame at Le Puy is a noted example) dating from llth to 12th century. But such are of Byzantine influence and the dome passes out as vaulting medium in the Roman esque while the tunnel vault comes into play, not as before with the Romans as culverts, drains, etc., but for vaulting the ceilings of therefore, takes the place of the groin. And this new method of vault construction inaugu rates the Gothic period. In the 12th century Gothic the former style of apse vaulting (hemi spherical) gave way to the chevet vault in which the masonry courses run perpendicularly, instead of horizontally, from radiating ribs having a common keystone. These run to a wall rib or line over the heads of the apse windows.