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People have been designing and building structures for thousands of years. Some of the structures that have survived longest and have become iconic are those that were erected for important religious functions, such as the great pyramids of Egypt and the temples of ancient India; those that served civic functions, such as the Roman forum; and those that had military purposes, such as the Great Wall of China. But, of course, at the same time, people were erecting countless short-lived buildings for everyday purposes such as dwellings, marketplaces, workshops, and stables.
Architecture has evolved mainly through the development of new materials and new principles of design. In the ancient world, the chief building materials were earth and wood (or bamboo) for short-lived structures and stone or brick for permanent structures. Ceramic tile was used for decorative purposes and for fireproof roof linings. Concrete was known to the Romans and used on some of the structures that have survived to this day, such as the Colosseum; however, its use was forgotten for many centuries after the Empire declined.
The most primitive design principle was the post and lintel: vertical supports, such as pillars or walls, holding up crossbeams. Columns spaced between the walls allowed architects to increase the amount of interior room, but the size of windows was severely limited by the load of the roof on the walls or on exterior columns. The invention of the arch allowed the supporting structures to be spaced farther apart; this technology was perfected by the Romans and, at roughly the same time, by the Chinese. The vault was essentially an elongated arch and the dome a circular arch. In the Middle East, the dome became an important form for buildings, and the principle of the arch was applied by military architects horizontally in the form of round fortifications that resisted the battering ram. In the West, another kind of arch, the flying buttress, permitted the construction of medieval cathedrals with much thinner walls than had previously been possible. This, plus improved manufacture of glass for windows, resulted in lighter and roomier interior spaces. Stained glass also served decorative and inspirational functions.
Another architectural element invented in ancient times was the truss, an arrangement that joins three structural members as a triangle. Because the three angles of the triangle cannot change unless one of the members is broken, the truss provides a lightweight but very rigid support. This structure allowed medieval architects to replace the vaulted roof with the triangular roof.
Few advances were made on these basic building technologies for centuries, during which changes in architectural styles were based mainly on changing aesthetic principles. The West, for example, went through a phase of highly decorative architecture during the Baroque period (St. Peter's in Rome is a good example) but later veered back toward the more restrained Neoclassical style (for example, Monticello).
The industrial revolution changed architecture by introducing iron, steel, and sheet glass as building materials. The Crystal Palace, constructed in London for the Great Exhibition of 1851, was a forerunner of modernist styles in the way that its design was largely determined by the decision to build the structure from large sheets of glass held on a metal frame. Later in that century, the development of structural steel members made it possible to apply this clean-line aesthetic to the ever-taller buildings we call skyscrapers. Other technologies that contributed to skyscrapers were the safety elevator, which Elisha Otis demonstrated at the Crystal Palace, and the telephone, which permitted communication between offices without the need for hordes of messenger boys clogging the elevators and hallways. Modernist designs also were applied to smaller buildings, such as the prairie houses of Frank Lloyd Wright.
More recent designs have shifted away from boxy geometric shapes and toward different visual effects. For example, the Sydney Opera House is designed to suggest the sails of boats in the adjacent harbor. Another recent trend is concern for environmental impact and sustainability, otherwise known as green building. Architects now pay increased attention to how much energy, water, and unrecyclable materials a building will require throughout its life cycle.