VOLTA. – Masonry roof structure, shaped in view as a curved surface and exerting a thrusting action on its supports (piers); in it one distinguishes the lower surface, visible from inside the space, called the intrados, and the upper surface, usually concealed by the roof or the floor of the space above, called the extrados.
According to the shape of the intrados, vaults are classified into several types, the principal ones being: barrel vault, generally used in rectangular spaces, formed by a cylindrical surface whose generatrices are normally parallel to the longer side, and whose directrix (i.e., the normal section) may be semicircular, or a depressed arch, or a pointed arch, or a multicentred arch; groin vault, used instead for spaces approximating a square, formed by the intersection of two cylindrical barrel vaults so that the walls are met along the directrices; pavilion vault, formed by the intersection of two such vaults, but with the walls met along the generatrices, thus being complementary to the preceding type; cloister vault, i.e., a pavilion vault truncated at the top by a horizontal plane; sail vault; and saucer vault, formed by a spherical calotte.
The vault originated from the need to cover large spaces with small elements that were easy to obtain or fabricate on site; this explains why it arose in the countries of the Middle East, which were poor in timber and ashlar stone. The Romans learned its construction from the Etruscans and then made it the typical structure of their architecture, from which it was inherited in Christian places of worship. The materials used were: brick, sometimes in special forms more suitable for execution; ashlar stone cut to appropriate shapes to accommodate the obliquity of the joints; and lightweight materials (e.g., in Byzantine architecture [V. BIZANTINA, ARTE, ARTE] special jars to reduce weight; plaster and similar materials in the 18th century, when the vault served a more decorative than structural function).
In religious architecture, the vault has been one of the determining elements of stylistic forms in all periods, both because it influenced the layout through the shaping and spacing of the supporting structures, and because it contributed to giving a special character to the interior of churches, especially in terms of vertical development.
Early Christian architecture generally did not use vaults, preferring in basilicas to have exposed roof structures; nonetheless, there are examples of annular vaults, i.e., barrel vaults with circular rather than straight generatrices, used in the space surrounding the central part—usually domed—of baptisteries and similar structures (e.g., S. Costanza in Rome).
Later, around the 11th century, the use of barrel vaults began to be revived, generally limited to chapels (e.g., S. Silvestro in SS. Quattro in Rome, the Assunta in S. Maria infra portas in Foligno), but sometimes adopted for covering entire buildings, especially in Umbria (e.g., S. Pietro di Bovara, S. Silvestro in Orvieto; in these last two churches the aisles are covered with half-barrel vaults), and more rarely in southern Italy (e.g., S. Margherita in Bisceglie), probably due to Eastern influences. Less frequently than in some countries north of the Alps, one finds reinforcing arches (arcs doubleaux) placed at more or less regular intervals with the aim of concentrating thrusts at suitable points when the supporting structures are discontinuous.
It was precisely these latter considerations that led to the invention of the groin vault, first used only in crypts (e.g., S. Eusebio in Pavia, S. Pietro in Tuscania, S. Vincenzo al Prato in Milan), then in the nave, but combined with other systems (with a dome in S. Babila in Milan, with a barrel vault in SS. Maria e Sigismondo in Rivolta d'Adda), and finally used alone (among the earliest examples, S. Ambrogio in Milan), a form that would become common by the second half of the 11th century. The main nave was then subdivided into regular intervals (bays) along its length to create square or nearly square spaces; and for the same purpose, the aisles were given twice as many bays, each corresponding to two in the main nave. With the groin vault, the type of Lombard church thus emerged, which would spread beyond the Alps.
A further refinement was introduced, still with the same aim, in the last years of the same century with the introduction of ribs (v.); the need to connect them with the supporting structures led to the replacement of columns with piers composed of a pillar to which bundles of small columns are attached; finally, the vault was made lighter so that the diagonal ribs, originally elliptical, became circular and in some cases even pointed. These arrangements, which appear sporadically in Italy in the course of the 12th century (cathedrals of Modena and Parma), were then fully developed in the 13th century. In the Renaissance, the groin vault was still used in some limited applications (e.g., S. Maria del Popolo in Rome), but with the elimination of ribs, thus simplifying the shape of the supports; yet the prevailing form—when a flat ceiling was not adopted—was the barrel vault, more in keeping with the new classical sentiment (e.g., Badia di Fiesole, S. Andrea in Mantua, S. Sisto in Piacenza). In the 16th century it became the usual form of roofing, transformed into a lunetted barrel vault (by the intersection of cylindrical vaults of lesser rise), which allowed windows to be opened above the side chapels to illuminate the nave, and at the same time to accentuate the rhythm of the bays (e.g., S. Maria dei Monti and Gesù in Rome, Il Redentore in Venice, etc.).
In the 17th century, however, and even more so in the 18th, Baroque conceptions—especially those of Borromini—aimed at replacing the simple Latin cross with more complex forms, also reflected in the type of roofing, which was no longer formed by the intersection of elementary geometric shapes but by the interpenetration of spheroids and ellipsoids, expressed in the intricate interweaving of ribs in various directions. Such arrangements were adopted especially in churches of Piedmont by Juvarra, Guarini, and Vittone, later spreading abroad, particularly to Germany and Austria, where they were in a sense linked to the tradition of stellar vaults from the late Gothic period, which, however, had found no application in Italy at that time.
During the Neoclassical period, alongside the frequent use of flat ceilings, the simple barrel vault was revived and continued throughout the 19th century.
Contemporary architecture, availing itself of the vast possibilities offered by reinforced concrete, has produced new forms based on concepts different from traditional ones, namely the so-called thin vaults of various types, examples of which can be seen in new churches in Pisa, Recoaro, Francavilla al Mare, and Milan, arising from competitions organized by the Pontifical Commission for Sacred Art, which promoted the study of new solutions of interest both constructively and aesthetically.
The decoration of vaults follows the vicissitudes of taste and artistic conditions in the various epochs. During the Paleo-Christian period it is entrusted predominantly to the mosaic, in the Romanesque and especially in the Gothic to fresco, particularly through large pictorial cycles. In the Renaissance it is generally decorated with coffers inspired by classical motifs (S. Andrea in Mantua) or with panels that follow the same motifs as the flat ceiling (sacristy of S. Spirito in Florence). In the second half of the 16th century the use of fresco is resumed, but in the form of large pictorial compositions (mostly glories of saints) to which the continuous surface of the barrel vault lends itself well; later stucco and gilding are associated with painting. The 18th century, on the other hand, prefers greater simplicity and reduces decorative richness, giving precedence to white stucco.