Arch and Vault, a fundamental construction system in architecture used to
span the space between walls, piers, or other supports and to create a roof
or a ceiling. Until the 19th century the arch and vault were the only
alternative to the far more limited and simpler post-and-lintel system
supporting a flat or peaked beamed roof.

Arch

An arch, in construction, is a rigid span curving upward between two points
of support. It appears in a variety of structures, such as an arcade,
formed by a row of arches, supported by load-bearing arches or a roof or a
bridge, or as a single, freestanding triumphal or memorial arch. The
traditional stone or brick arch, formed of many segments held in place by
lateral thrust, was developed to connect a greater distance between two
supports than a single horizontal beam, or lintel, could bridge. Since the
19th century, arches have also been made of single, curved spans of iron,
steel, or reinforced concrete.

The masonry arch has many elements. Its supports may be walls, piers, or
columns, and the capstones from which it springs are known as imposts. The
upper part of the arch is the crown, the portions near the impost are the
haunches, its wedge-shaped segments are voussoirs, and the central or
crowning voussoir is the keystone. The inner edge of the arch is the
intrados; the outer edge, the extrados; and the undersurface, the soffit.
The molded band that often is found around the opening of the arch is the
archivolt. The wall spaces on either side of an arch, or between adjacent
arches, are spandrels. If the space between the arch and the lintel is
filled in, the resulting flat surface is the tympanum. Arches have been
built since prehistoric times. Rude prototypes were made by leaning two
slabs of rock together or by constructing a stepped, or corbeled, arch in
which projecting elements from a wall rise in steps from the supports to
meet in the center. The Egyptians, Babylonians, and Greeks used the arch,
generally for secular structures, such as storerooms and sewers. The
Assyrians built palaces with arched ceilings, and the Etruscans used arches
in bridges, passageways, and gates. The Romans, however, were the first to
develop the arch on a massive scale. They used the semicircular arch freely
in secular structures such as amphitheaters, ...