Akademik

   The arch was invented around 2500 BC in the Indus Valley of ancient India. It is a curved structure that rests on posts or walls and allows for the spanning of an architectural space. Prior to the use of the arch, the post-and-lintel structure provided for such spatial en-closures. The arch is technically superior to the post-and-lintel because its curvature directs the weight of the structural materials, usually stone, as well as gravity, more forcefully toward the posts or walls rather than upon a straight lintel.

   The arch gradually developed from simple corbelling to corbelling that culminated in a keystone. Corbelling is found in the Prehistoric era around 3000 BC in such buildings as those in the Neolithic village of Skara Brae on the Orkney Islands off the coast of Scotland. Here the walls are made of layers of flat stones stacked up and gradually sloped inward to a small opening that would probably have been covered with thatching or left open above the interior hearth. The most famous use of the keystone is found in the Mycenaean Lion Gate (1250 BC) located in the Ancient Aegean citadel of Mycenae in the Peloponnese of Greece. Here an inverted triangular-shaped stone carved with two lions is located above a slightly curved lintel over the entranceway. This keystone encourages the dispersal of weight into the side walls rather than over the entrance void.

   Although prototypes of the arch were widespread, appearing in the Ancient Near Eastern, Ancient Egyptian, and Etruscan cultures, it was not until Ancient Rome that its use became fully developed in the repetition of an arch to create a barrel vault, in the intersection of two barrel vaults at a 90-degree angle to create a cross vault, and finally, in spinning an arch on its axis to create the dome. Roman arches were semicircular and built with special arch bricks called voussoirs that were capped by a keystone. Typical are the arches found on the Ancient Roman aqueduct called the Pont du Gard in Nîmes, France, from the late first century BC, in which three registers of such arches traverse 30 miles over uneven terrain to reach its destination, bringing water at three different levels to the city of Nîmes. Arched bridges were not only stronger than a masonry wall, but also more economical.

   Furthermore, by repeating an arch to span not just the width but also the length of a structure, the Ancient Romans were able to create vast interior halls with tall arched ceilings. Trajan's market in Rome, from the second century AD, demonstrates the use of a concrete barrel vault to cover a building and provide for a long interior hallway uncluttered with supporting columns. The Basilica of Maxentius and Constantine, built in Rome in the fourth century AD, reveals the use of two intersecting barrel vaults to create a cross-vault, also called a groin vault because of the groin-like angles. Sometimes the groin vault is articulated with ribbing and thus is often called a ribbed vault. The vast ceiling of the basilica is covered by three massive groined vaults. More intricate vaulting systems can be found in the Baths of Caracalla, built in Rome in the early third century AD. The vaulting system of Ancient Roman bathhouses may have been based on even earlier vast underground water storage and drainage systems.

   The semicircular arch continued to be used in Early Medieval, Romanesque, and then Gothic architecture, when the pointed arch was introduced. The pointed arch allows for an increase in height and was usually employed in the clerestory windows of a Gothic church to increase the dimensions of the fenestration and therefore the amount of light that enters the building. Because glass windows are inherently weaker than a masonry wall, the flying buttress support system was then introduced on the exterior of the Gothic cathedral to provide the additional support needed for the tall walls. The pointed arch also assumed an important symbolic meaning, as it more explicitly draws the eye upward toward the heavens.

   The pointed arch may have originated in Assyrian architecture, and certainly variations such as the horseshoe arch were widespread prior to the Gothic period. The horseshoe arch, which appears to be pinched inward at the impost blocks, has traditionally been considered an Islamic invention, but it first appeared in ancient Indian architecture. Then in western Europe — in Burgos, Spain, for example—the horseshoe arch is found in Visigothic buildings such as in the entrance doorway of the Church of Santa Maria de Quintanilla de las Viñas, built by Visigothic Arian Christians in the late seventh century. The double arch is another way in which the height of a wall can be increased. Double arches are found in the 780s in Islamic architecture, as in the Great Mosque at Cordoba, Spain. Here, the arch is not used to span a large, unencumbered space, but rather, as double arches, they link together a densely colonnaded in-terior courtyard and allow for a greater circulation of air in this hotter climate.

   Parabolic, or catenary, arches are structurally superior, and were not introduced until the modern age of architecture. The Catalonian architect Antoni Gaudí is credited with creating the catenary arch, a more steeply curved form that directs all horizontal thrust down into the posts or walls and therefore does not need additional systems of support. Constructing the arch from voussoirs or other individual materials attached together perpendicular to the curvature of the arch minimizes the shear stress at the joints, and therefore the thrust is more effectively directed into the ground, following the line of the arch. In his Cathedral of Sagrada Familia, begun in Barcelona in 1884 and not yet finished, are a series of catenary arches that recall the pointed Gothic arch but provide a superior support system. The St. Louis Gateway Arch, built by Eero Saarinen in the 1960s, is perhaps the most famous catenary arch. Here, the 630-feet tall arch is shaped into equilateral triangles, and made of stainless steel over reinforced concrete.

   Finally, the inverted parabolic arch is also employed in the suspension bridge, where the catenary arch is attached at intervals to create a parabola. Simple suspension bridges can be found as early as AD 100 and can be seen in the ancient Inca rope bridges, but modern suspension bridges developed out of the truss arch bridge to span several miles. Perhaps the most famous suspension bridge is the Golden Gate Bridge in San Francisco, built in 1937 based on the original idea by Joseph Strauss; it was at the time the longest bridge in the world. New materials and more sophisticated mathematical calculations will continue to provide more functional and aesthetic possibilities for the use of the arch in architectural construction.

   See also PANTHEON, ROME.