Arch (architecture)

An arch is a curved architectural structure that spans an opening and functions as a support for the weight above it. The first arches were developed more than four thousand years ago, although it was not until the time of the ancient Romans that the structure was widely used in large-scale engineering projects. The Romans improved upon the design of the arch, allowing it to be used to support bigger structures and influencing architecture for centuries. There are many variations and shapes of arches, but the physics of the structure—distributing the weight outward instead of downward—remains constant.

Brief History

The earliest arches were used in Mesopotamian architecture sometime in the second millennium B.C.E. Because of their limitations, these first arches were mostly utilized to support small structures such as storerooms and underground drains. The Egyptians and Greeks also employed the arch as a small-scale support structure. They used a series of columns as a means to support larger weights such as roofs.

The ancient Romans adopted the arch from the Etruscans, the civilization that preceded them on the Italian peninsula. The Romans improved upon the design by flattening the shape of the arch and using them at intervals during constriction to create larger structures able to support more weight. They were able to do this thanks to the invention of a form of concrete, a mixture of a calcium-based mineral called lime and volcanic ash and rocks that provided a durable construction material. The Romans utilized the arch to create large aqueducts, bridges, and structures, including some of the most famous works of Roman architecture. The Roman Colosseum, a three-story amphitheatre completed in the first century C.E., utilized about two hundred arches in its construction. Roman leaders built numerous stand-alone triumphal arches to celebrate military victories and other significant events. The Romans also adapted the design of the arch, combining a series of arches into a ceiling or roof known as a vault. An arch that extends for 360 degrees is called a dome. These three elements—the arch, vault, and dome—revolutionized architecture and were adopted by other cultures across the ancient and modern worlds.

Overview

Arches are able to support heavier loads than rectangular openings and columns because the arch dissipates the force of the weight above it outward. Columns and other shapes distribute the force downward, putting more pressure on the supports. Arches channel the force of the weight into compressive stress, compacting the blocks into each other and distributing weight into the ground. The wedge-shaped blocks used to construct an arch are called voussoirs. The central stone at the apex of the arch is called the keystone. The keystone is the last block placed during construction of an arch, locking the other pieces into position and distributing the weight above through the blocks on either side. Upon completion of the arch, the keystone is often given ceremonial importance and may be larger than the surrounding voussoirs or adorned with decoration. There are many different styles of arches, but these usually fall into three basic forms: circular, pointed, or parabolic—a curved, symmetrical shape resembling the letter U.

One of the earliest forms of an arch was the corbel arch. The blocks in this type of structure were placed progressively inward until they met at the keystone. Corbel arches have been found in Egyptian and Mesopotamian architecture dating back to almost 2000 B.C.E. The rounded or Roman-style arch is a design that forms a semicircle. As the name implies, this form was used in ancient Rome and is one of the most commonly used styles in history. Architects of the Italian Renaissance often employed the Roman arch in their designs. A more modern example of a Roman arch is the Arc de Triomphe in Paris. The structure was constructed by Napoleon in the nineteenth century as a symbol that his military victories surpassed those of Julius Caesar.

The distinctive Moorish or horseshoe arch was a style created in the Islamic world and used in building mosques and palaces. This style narrows in at a point before widening into a round or pointed semicircle top. The Great Mosque of Cordoba, built in the eighth century in Spain, was constructed with this type of arch. Christian cathedrals of the medieval period used a thinner, pointed design known as the Gothic arch. These arches were a staple of what would become known as Gothic architecture and can be seen in the design of the thirteenth-century Chartres Cathedral in France.

The ogee arch resembled the Gothic style but featured a pointed top with two S-shaped curves on both sides. This design was introduced in the late Middle Ages and was used extensively in England of the thirteenth and fourteenth centuries. Tudor-style arches are also related to Gothic arches. They maintain a small point at the crown but also have a wider and flatter span. This form of arch was developed during the English Tudor period, which lasted from the fifteenth to the seventeenth century.

Among notable modern structures, the world's tallest arch is the Gateway Arch in St. Louis, Missouri. The 630-foot parabolic arch was built in the 1960s as a monument to the westward expansion of the United States in the nineteenth century. The span was constructed from 142 pieces of steel and more than 23,000 tons of concrete. The largest arch bridge in the world is China's Chaotianmen Bridge, which spans 1,811 feet. In the United States, the New River Gorge Bridge in West Virginia measures 1,700 feet.

Bibliography

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Inamdar, Niraj. "A Brief Overview of the Techniques of Vaulted Architecture in Rome." Massachusetts Institute of Technology, web.mit.edu/inamdar/www/Site/Publications‗and‗Science‗files/Roman‗Vaults‗Inamdar.pdf. Accessed 14 Nov. 2016.

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Sinclair, Leah. "The History of Architecture in Eleven Arches." Architectural Review, 19 Dec. 2014, www.architectural-review.com/archive/the-history-of-architecture-in-eleven-arches/8673174.article. Accessed 14 Nov. 2016.

Strickland, Carol. The Annotated Arch: A Crash Course in the History of Architecture. Andrews McMeel Publishing, 2001.