tower, structure, the greatest dimension of which is its height. Towers have belonged to two general types. The first embodies practical uses such as defense (characteristic of the Middle Ages), to carry bells, beacons, or antennas, and to utilize maximum floor space in a given area, as in modern skyscrapers. The second type is used to symbolize the authority and power of religious and civic bodies, as in the churches and town halls of Europe; skyscrapers also perform a similar function for modern corporations. The earliest use of tall structures for ritual and symbolism is seen in the Babylonian ziggurat. The temple architecture of India had a variety of pyramidal and cylindrical masonry towers. The many-storied pagoda in wood was a part of early Chinese and Japanese temple architecture. The minaret belongs to Islamic religious architecture. Used for defensive purposes in the early Middle Ages in Western Europe, towers with massive masonry walls served as refuges and lookouts. Many 9th- and 10th-century round defense towers remain in Ireland and a few in Scotland, including one at Brechin. Castles had their donjons or keeps, of which the 11th-century Tower of London shows a high development. Of the fortified towers that Italian nobles built even for their city dwellings numerous examples remain, notably at San Gimignano. The earliest existing church towers in Europe were those of the 5th and 6th cent. in Ravenna, Italy. There the bell tower, or campanile, stood detached from the church building itself; another example is the celebrated bell tower at Pisa (1174). In English and French Romanesque churches a high tower rises over the crossing of nave and transepts, and the west end generally possesses lower twin towers. The relatively simple Romanesque towers generally had square or round shafts with many blind arcades in horizontal tiers and were topped by a simple octagonal or conical spire. They developed into the higher, elaborate type of Gothic, decorated with pinnacles and canopied niches. Towers of extreme lightness and intricacy were developed in the late Gothic period, as in the cathedrals at Rouen, Vienna, and Antwerp. With the Renaissance the classical orders were incorporated into tower design. Particular success was attained in the tapering pyramidal compositions of Sir Christopher Wren's numerous London towers, including those of St. Paul's Cathedral. English churches, e.g., St. Martin-in-the-Fields by James Gibbs, set the pattern for the typical New England church with the wooden tower and steeple rising directly over the entrance vestibule. In the 20th cent. towers have often taken the form of skyscrapers. Notable modern towers of varied design and function include the highly original Einstein Tower at Potsdam by Erich Mendelsohn and Frank Lloyd Wright's Johnson tower with glass tubing at Racine, Wis.

Tower of London, ancient fortress in London, England, just east of the City and on the north bank of the Thames, covering about 13 acres (5.3 hectares). Now used mainly as a museum, it was a royal residence in the Middle Ages. Later it was a jail for illustrious prisoners. The Tower is enclosed by a dry moat, within which are double castellated walls surrounding the central White Tower. Although Roman foundations have been discovered, the White Tower was built c.1078 by Gundulf, bishop of Rochester; the exterior was restored by Sir Christopher Wren. Various towers subsequently built were used as prisons; one of them now houses a collection of medieval arms and armor. The crown jewels are displayed in the Waterloo Block, a former barracks. The Traitors' Gate (giving access by water from the Thames) and the Bloody Tower are associated with many historically noted persons, including Queen Elizabeth I (when still princess), Sir Thomas More, Anne Boleyn, Catherine Howard, Lady Jane Grey, the 2d earl of Essex, Sir Walter Raleigh, and the duke of Monmouth. Many persons beheaded within the Tower precincts, or on the neighboring Tower Hill, were buried in the Chapel of St. Peter ad Vincula. The Yeomen of the Guard ("Beefeaters"), dressed in Tudor garb, still guard the Tower.

Tower Hamlets, inner borough (1991 pop. 153,500), of Greater London, SE England. Tower Hamlets was formed in 1965 by the merger of the metropolitan boroughs of Bethnal Green, Poplar, and Stepney. The southern boundary of Tower Hamlets fronts on the Thames and includes some of London's busiest docks. The borough's industries include furniture making, dressmaking, and brewing. The Tower of London and the Canary Wharf financial center are located in the borough.

Sears Tower, Chicago, the world's third tallest building. Until the opening of the 1,483-ft (452-m) Petronas Towers (1997) in Kuala Lumpur, Malaysia, it was the world's tallest building. Constructed from 1970 to 1974 for Sears, Roebuck & Co., it rises 110 stories to a height of 1,450 ft (442 m); the 253 ft (77 m) television antenna topping it makes it the world's third largest freestanding structure at 1,703 ft (519 m). Designed by the firm of Skidmore, Owings and Merrill, the Sears Tower is supported structurally by square tubes of welded steel with floors suspended within the tubes, a technological innovation that was developed specifically for the mammoth skyscraper by architectural engineer Fazlur Kahn. The Sears Tower has an exterior of black aluminum and bronze-toned glass cut by black bands.

Eiffel Tower, structure designed by A. G. Eiffel and erected in the Champ-de-Mars for the Paris exposition of 1889. The tower is 984 ft (300 m) high and consists of an iron framework supported on four masonry piers, from which rise four columns uniting to form one shaft. Three platforms at different heights (the intermediate platform just above the junction of the columns is 644 ft/196 m high) are reached by stairs and elevators. On the top of the tower are a meteorological station, a wireless station, and a television transmission antenna.

Devils Tower National Monument, 1,347 acres (546 hectares), overlooking the Belle Fourche River, NE Wyo.; it was the first designated U.S. national monument (1906). Devils Tower, 865 ft (264 m) high and narrowing in width from 1,000 ft (305 m) at its base to 250 ft (76 m) at its summit, is a cluster of rock columns formed by the cooling and crystallization of molten matter. Geologists assume it to be a remnant of an ancient lava intrusion into sedimentary strata which were later removed by wind and water action, leaving the more resistant "tower" to dominate the skyline. Sacred to many Lakota, Cheyenne, and members of other Plains tribes, who call it Bear Lodge, it is also a popular rock-climbing and tourist site, which has caused some controversy. See National Parks and Monuments, table.

Any freestanding or attached structure that is relatively tall in proportion to its base. The Romans, Byzantines, and medieval Europeans built defensive towers as part of the fortifications of their city walls (e.g., the Tower of London). Indian temple architecture uses towers of various types (e.g., the sikhara). Towers were an important feature of churches and cathedrals built in the Romanesque and Gothic periods. Some Gothic church towers were designed to carry a spire; others had flat roofs. The Italian campanile could either be attached to a church or freestanding. The use of towers declined somewhat during the Renaissance but reappeared in Baroque architecture. The use of steel frames enabled buildings to reach unprecedented heights; the Eiffel Tower in Paris was the first structure to reveal the true vertical potential of steel construction.

Learn more about tower with a free trial on Britannica.com.

Bell tower, either freestanding or attached to another structure. More particularly it refers to the room, usually at the top of such a tower, where the bells and their supporting timberwork are hung. The belfry is a prominent feature of Belgian Gothic architecture, especially in Flanders. The Halles (Market Hall) and belfry in Brugge (late 13th century) is a typical example. The term derives from the medieval siege tower (berfrei), a tall wooden structure that could be rolled up to a fortification wall so that the warriors hidden inside could storm the battlements.

Learn more about belfry with a free trial on Britannica.com.

Royal fortress on the northern bank of the River Thames. The central keep, or donjon, known as the White Tower because of its limestone, was begun circa 1078 by William I the Conqueror inside the Roman city wall. In the 12th–13th century the fortifications were extended beyond the wall, the White Tower becoming the nucleus of a series of concentric defenses. The only entrance from the land is at the southwestern corner; when the river was still a major highway, the 13th-century water gate was much used. Its nickname, Traitors' Gate, derives from the prisoners brought through it to the Tower, long used as a state prison; many were murdered or executed there.

Learn more about Tower of London with a free trial on Britannica.com.

Skyscraper office building in Chicago. With 110 floors and a height of 1,450 ft (442 m), it became the world's tallest building at its completion in 1974. Its architect, Fazlur Khan (1928–1982), designed it as a bundled-tube (see skyscraper) structure to resist lateral forces. It is modular in plan, with nine 75-ft- (23-m-) square, column-free units. The exterior is sheathed in black aluminum and bronze-tinted glass. Louvers clad the four floors devoted to the building's mechanical operations. It was the world's tallest building until 1996, when it was surpassed by the Petronas Towers (1,483 ft [452 m]) in Kuala Lumpur, Malaysia.

Learn more about Sears Tower with a free trial on Britannica.com.

Parisian landmark built for the Centennial Exposition of 1889. Conceived by the bridge engineer Gustave Eiffel (1832–1923), the 984-ft (300-m) tower of open-lattice wrought iron was a technological masterpiece. Making use of advanced knowledge of the behaviour of metal arch and truss forms under loading, the structure presaged a revolution in civil engineering and architectural design. The tower was the world's tallest building until the Chrysler Building in New York City was topped off in 1929.

Learn more about Eiffel Tower with a free trial on Britannica.com.

National preserve, northeastern Wyoming, U.S. The first U.S. national monument, it was established in 1906 near the Belle Fourche River. It includes 1,347 acres (545 hectares) and features a natural rock tower, the remnant of a volcanic intrusion now exposed by erosion. The tower has a flat top and is 865 ft (264 m) high.

Learn more about Devils Tower National Monument with a free trial on Britannica.com.