A tower is a tall

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

, taller than it is wide, often by a significant factor. Towers are distinguished from masts by their lack of guy-wires and are therefore, along with tall buildings, self-supporting structures. Towers are specifically distinguished from buildings in that they are built not to be habitable but to serve other functions using the height of the tower. For example, the height of a

clock tower Clock towers are a specific type of structure which house a turret clock and have one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also adjoin or be located on top of another buildi ...

improves the visibility of the clock, and the height of a tower in a fortified building such as a

castle A castle is a type of fortified structure built during the Middle Ages predominantly by the nobility or royalty and by military orders. Scholars debate the scope of the word ''castle'', but usually consider it to be the private fortified r ...

increases the visibility of the surroundings for defensive purposes. Towers may also be built for

observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The ...

, leisure, or telecommunication purposes. A tower can stand alone or be supported by adjacent buildings, or it may be a feature on top of a larger structure or building.

Etymology

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...

''torr'' is from Latin ''turris'' via Old French ''tor''. The Latin term together with Greek τύρσις was loaned from a pre-Indo-European Mediterranean language, connected with the Illyrian toponym Βου-δοργίς. With the Lydian toponyms Τύρρα, Τύρσα, it has been connected with the ethnonym Τυρρήνιοι as well as with ''Tusci'' (from ''*Turs-ci''), the Greek and Latin names for the Etruscans (Kretschmer Glotta 22, 110ff.)

History

Towers have been used by mankind since prehistoric times. The oldest known may be the circular stone tower in walls of Neolithic Jericho (8000 BC). Some of the earliest towers were ziggurats, which existed in

Sumerian architecture The architecture of Mesopotamia is ancient architecture of the region of the Tigris–Euphrates river system (also known as Mesopotamia), encompassing several distinct cultures and spanning a period from the 10th millennium BC (when the first perm ...

since the 4th millennium BC. The most famous ziggurats include the Sumerian Ziggurat of Ur, built in the 3rd millennium BC, and the

Etemenanki Etemenanki ( Sumerian: "temple of the foundation of heaven and earth") was a ziggurat dedicated to Marduk in the ancient city of Babylon. It now exists only in ruins, located about south of Baghdad, Iraq. Etemenanki has been suggested to be th ...

, one of the most famous examples of Babylonian architecture. Some of the earliest surviving examples are the

broch A broch is an Iron Age drystone hollow-walled structure found in Scotland. Brochs belong to the classification "complex Atlantic roundhouse" devised by Scottish archaeologists in the 1980s. Their origin is a matter of some controversy. Origin ...

structures in northern Scotland, which are conical tower houses. These and other examples from Phoenician and Roman cultures emphasised the use of a tower in fortification and sentinel roles. For example, the name of the Moroccan city of

Mogador Essaouira ( ; ar, الصويرة, aṣ-Ṣawīra; shi, ⵜⴰⵚⵚⵓⵔⵜ, Taṣṣort, formerly ''Amegdul''), known until the 1960s as Mogador, is a port city in the western Morocco, Moroccan region of Marrakesh-Safi, Marakesh-Safi, on the ...

, founded in the first millennium BC, is derived from the Phoenician word for watchtower ('migdol'). The Romans utilised octagonal towers as elements of Diocletian's Palace in Croatia, which monument dates to approximately 300 AD, while the Servian Walls (4th century BC) and the Aurelian Walls (3rd century AD) featured square ones. The Chinese used towers as integrated elements of the Great Wall of China in 210 BC during the Qin Dynasty. Towers were also an important element of castles. The Eiffel Tower, Paris, France

Other well known towers include the Leaning Tower of Pisa in

Pisa, Italy Pisa ( , or ) is a city and ''comune'' in Tuscany, central Italy, straddling the Arno just before it empties into the Ligurian Sea. It is the capital city of the Province of Pisa. Although Pisa is known worldwide for its leaning tower, the cit ...

built from 1173 until 1372, the Two Towers in Bologna, Italy built from 1109 until 1119 and the

Towers of Pavia Characteristic of the historic center of Pavia is the presence of medieval noble towers that survive in its urban fabric, despite having once been more numerous, as evidenced by the sixteenth-century representation of the city frescoed in the chu ...

(25 survive), built between 11th and 13th century. The Himalayan Towers are stone towers located chiefly in Tibet built approximately 14th to 15th century. Dana Thomas, "Towers to the Heavens"
''Newsweek'', 2003-11-15

Mechanics

Up to a certain height, a tower can be made with the supporting structure with parallel sides. However, above a certain height, the compressive load of the material is exceeded, and the tower will fail. This can be avoided if the tower's support structure tapers up the building. A second limit is that of buckling—the structure requires sufficient stiffness to avoid breaking under the loads it faces, especially those due to winds. Many very tall towers have their support structures at the periphery of the building, which greatly increases the overall stiffness. A third limit is dynamic; a tower is subject to varying winds, vortex shedding, seismic disturbances etc. These are often dealt with through a combination of simple strength and stiffness, as well as in some cases tuned mass dampers to damp out movements. Varying or tapering the outer aspect of the tower with height avoids vibrations due to vortex shedding occurring along the entire building simultaneously.

Functions

Although not correctly defined as towers, many modern

high-rise building A tower block, high-rise, apartment tower, residential tower, apartment block, block of flats, or office tower is a tall building, as opposed to a low-rise building and is defined differently in terms of height depending on the jurisdictio ...

s (in particular

skyscraper A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ris ...

) have 'tower' in their name or are colloquially called 'towers'. Skyscrapers are more properly classified as 'buildings'. In the United Kingdom, tall domestic buildings are referred to as tower blocks. In the United States, the original World Trade Center had the nickname the Twin Towers, a name shared with the Petronas Twin Towers in Kuala Lumpur. In addition some of the structures listed below do not follow the strict criteria used at List of tallest towers.

Strategic advantages

The tower throughout history has provided its users with an advantage in surveying defensive positions and obtaining a better view of the surrounding areas, including battlefields. They were constructed on defensive walls, or rolled near a target (see siege tower). Today, strategic-use towers are still used at prisons, military camps, and defensive perimeters.

Potential energy

By using gravity to move objects or substances downward, a tower can be used to store items or liquids like a storage silo or a water tower, or aim an object into the earth such as a

drilling tower A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill wat ...

. Ski-jump ramps use the same idea, and in the absence of a natural mountain slope or hill, can be human-made.

Communication enhancement

In history, simple towers like

lighthouse A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways. Lighthouses mar ...

bell tower A bell tower is a tower that contains one or more bells, or that is designed to hold bells even if it has none. Such a tower commonly serves as part of a Christian church, and will contain church bells, but there are also many secular bell tower ...

s, signal towers and

minaret A minaret (; ar, منارة, translit=manāra, or ar, مِئْذَنة, translit=miʾḏana, links=no; tr, minare; fa, گل‌دسته, translit=goldaste) is a type of tower typically built into or adjacent to mosques. Minarets are generall ...

s were used to communicate information over greater distances. In more recent years, radio masts and cell phone towers facilitate communication by expanding the range of the transmitter. The CN Tower in Toronto, Ontario, Canada was built as a communications tower, with the capability to act as both a transmitter and repeater.

Transportation support

Towers can also be used to support bridges, and can reach heights that rival some of the tallest buildings above-water. Their use is most prevalent in

suspension bridge A suspension bridge is a type of bridge in which the deck (bridge), deck is hung below suspension wire rope, cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridg ...

s and cable-stayed bridges. The use of the pylon, a simple tower structure, has also helped to build railroad bridges, mass-transit systems, and harbors.

Control tower Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

s are used to give visibility to help direct aviation traffic.

Other

* To access tall or high objects: launch tower,

service tower A service structure is a steel framework or tower that is built on a rocket launch pad to facilitate assembly and servicing. An umbilical tower also usually includes an elevator which allows maintenance and crew access. Immediately before igniti ...

, service structure, scaffold, tower crane. * To access atmospheric conditions aloft: wind turbine, meteorological

measurement tower A measurement tower or measurement mast, also known as meteorological tower or meteorological mast (met tower or met mast), is a free standing tower or a removed mast, which carries measuring instruments with meteorological instruments, such as ...

tower telescope A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum. Obsolete names for Sun telescopes include heliograph and photoheliograph ...

, solar power station * To lift high tension cables for electrical power distribution transmission tower * To take advantage of the temperature gradient inherent in a height differential: cooling tower * To expel and disperse potentially harmful gases and particulates into the atmosphere:

chimney A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typic ...

* To protect from exposure:

BREN Tower BREN Tower was a guyed steel framework mast, high, on the Nevada Test Site in Nevada, USA. "BREN" stands for "Bare Reactor Experiment, Nevada." The structure was owned by the Department of Energy and maintained by National Security Technologies ...

lightning rod tower A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the rod and be conducte ...

* For industrial production: shot tower * For surveying: Survey tower * To drop objects:

Drop tube In physics and materials science, a drop tower or drop tube is a structure used to produce a controlled period of weightlessness for an object under study. Air bags, polystyrene pellets, and magnetic or mechanical brakes are sometimes used to a ...

(drop tower), bomb tower, diving platform * To test height-intensive applications:

elevator test tower An elevator test tower is a structure usually 100 to over 200 metres (300 feet to over 600 feet) tall that is designed to evaluate the stress and fatigue limits of specific elevator cars in a controlled environment. Tests are also carried out in ...

* To improve structural integrity:

thyristor tower A valve hall is a building which contains the valves of the static inverters of a high-voltage direct current plant. The valves consist of thyristors, or at older plants, mercury arc rectifiers. Mercury arc rectifiers are usually supported by i ...

* To mimic towers or provide height for training purposes: fire tower,

parachute tower A parachute tower is a tower used for parachute training, often by members of a military paratroop unit. A mixture of tower heights are used at different stages of training. Trainees typically begin on towers around in height in fall-arrest harn ...

* As art: Shukhov Tower * For recreation: rock climbing tower * As a symbol: Tower of Babel, The Tower (Tarot card),

church tower Church may refer to: Religion * Church (building), a building for Christian religious activities * Church (congregation), a local congregation of a Christian denomination * Church service, a formalized period of Christian communal worship * Chris ...

The term "tower" is also sometimes used to refer to firefighting equipment with an extremely tall ladder designed for use in firefighting/rescue operations involving high-rise buildings.

Gallery

References

External links

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