arch - A structure with a curved, pointed, or squared upper edge to an opening, and supporting the weight above it (as in this link to a picture of elementary students creating a catenary arch.) It is usually a masonry construction, used as a doorway, window, or a portal, although freestanding monumental arches have been built simply for symbolic purposes.

Some arches, most of them monumental:

Babylonia, The Ishtar-Gate of Babylon, 6th century BCE, glazed brick construction. Near-Eastern Museum, Berlin. It was Babylonia's King Nebuchadnessar II who captured (597) and destroyed (588) Jerusalem and carried the Israelites into captivity in Babylon. See relief.

Roman, Pont du Gard Aqueduct, near Nimes, France, c. 20-10 BCE. See aqueduct and Roman art.

Roman Colosseum, or Flavian Amphitheater, 70-82 CE, a vast ellipse with tiers of seating for 50,000 spectators around a central elliptical arena. The façade of three tiers of arches and an attic story is about 48.5 m (158 feet) tall. The three tiers of arcades are faced by three-quarter columns and entablatures, Doric in the first story, Ionic in the second, and Corinthian in the third. The construction utilized a careful combination of types: concrete for the foundations, travertine for the piers and arcades, tufa infill between piers for the walls of the lower two levels, and brick-faced concrete used for the upper levels and for most of the vaults.

Arch of Titus, in the Forum of Rome, built in 81 CE to commemorate the capture of Jerusalem. Although massive, it was well proportioned in order to minimize its weight. The Arch of Titus is located the eastern edge of the forum and was used as one of its principal entrances. In ancient times, soldiers returning from victories in war or battle marched ceremoniously through this arch and through the forum to the cheers of the populace. The arch is carved with relief sculptures of the victory in Jeruselum. One of them shows a parade in which the victors carry spoils from the Temple.

Roman, in the Forum of Rome, Arch of Septimius Severus, 203 CE, bearing masonry. Another classic example of a triumphal arch. Another view, including much of the Roman Forum around the arch.

John Sell Cotman (English, 1782-1842), Crypt in the Church of St. Gervais, Rouen, 1819, pencil and wash on paper, 18.4 x 27.6 cm, Tate Gallery, London. See crypt.

John Nash (English, 1752-1835), Marble Arch, 1828, Oxford Street, London. The Marble Arch was built in as the chief entrance to Buckingham Palace, but it was too narrow for royal coaches, so when the palace was extended in 1851, the arch was moved to its current site as an entrance to Hyde Park. By tradition, only senior members of the royal family, the King's Troop and the Royal Horse Artillery are allowed to ride or drive through the Arch.

John Augustus Roebling (American, 1806-1869), Brooklyn Bridge, 1869-1883, suspension bridge with steel cable, and stone masonry piers. Completed by John's son, Washington Augustus Roebling.

McKim, Mead & White, Washington Arch, 1889 / 91, marble, New York, NY. Inspired by Roman triumphal arches, this structure was first erected as a temporary structure made of wood and stucco in 1889 to celebrate the centennial of George Washington's inauguration. The design was rebuilt in marble in 1891. Decorated with sculptures of Washington in both his civilian and military guises by Alexander Stirling Calder (American, 1870-1945) and Herman MacNeil. In the first decades of the 20th century, the West Village became an increasingly bohemian neighborhood, and the arch became a site of artistic and social activism.

A masonry arch has a keystone surmounting and holding in place several wedge-shaped blocks, called voussoirs, that transmit the downward pressure laterally. A diaphragm arch is a transverse, wall-bearing arch that divides a vault or a ceiling into compartments, providing a kind of fire-break. Arches may take different shapes, as in the pointed Gothic arch, the rounded Roman or Romanesque arch, or the stilted Islamic arch, but all require support from other arches or buttresses.

Also see arcade, architecture, centering, fenestration, impost block, spandrel, springing, and thrust.

Other works in which arches are featured:

Francesco Guardi (Italian, 1712-1793), Triumphal Arch on the Embankment, Venice, pen and brown ink with brown wash, watercolor, heightened with white, 28 x 19.1 cm, Hermitage Museum, St. Petersburg, Russia.

Hubert Robert (French, 1733-1808), The Return of the Cattle, oil on canvas, 80 3/4 x 48 inches (205.1 x 121.9 cm), Metropolitan Museum of Art, NY. See Rococo.