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A tower is a tall structure, taller than it is wide, often by a significant factor. Towers are distinguished from by their lack of and are therefore, along with tall buildings, self-supporting structures.

Towers are specifically distinguished from in that they are built not to be habitable but to serve other functions using the of the tower. For example, the height of a improves the visibility of the clock, and the height of a tower in a fortified building such as a increases the visibility of the surroundings for defensive purposes. Towers may also be built for observation, 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
torr is from turris via tor. The Latin term together with τύρσις was loaned from a pre-Indo-European Mediterranean language, connected with the Illyrian toponym Βου-δοργίς. With the toponyms Τύρρα, Τύρσα, it has been connected with the ethnonym as well as with Tusci (from *Turs-ci), the Greek and Latin names for the (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 , which existed in Sumerian architecture since the 4th millennium BC. The most famous ziggurats include the Sumerian Ziggurat of Ur, built in the 3rd millennium BC, and the , one of the most famous examples of Babylonian architecture.

Some of the earliest surviving examples are the structures in northern , which are conical . These and other examples from and cultures emphasised the use of a tower in fortification and sentinel roles. For example, the name of the Moroccan city of , founded in the first millennium BC, is derived from the Phoenician word for ('migdol'). The Romans utilised octagonal towers as elements of Diocletian's Palace in , which monument dates to approximately 300 AD, while the (4th century BC) and the (3rd century AD) featured square ones. The Chinese used towers as integrated elements of the Great Wall of China in 210 BC during the . Towers were also an important element of castles.

Other well known towers include the Leaning Tower of Pisa in Pisa, Italy built from 1173 until 1372, the Two Towers in Bologna, Italy built from 1109 until 1119 and the Towers of Pavia (25 survive), built between 11th and 13th century. The are stone towers located chiefly in 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 buildings (in particular ) have 'tower' in their name or are colloquially called 'towers'. Skyscrapers are more properly classified as 'buildings'. In the , tall domestic buildings are referred to as tower blocks. In the , the original World Trade Center had the nickname the Twin Towers, a name shared with the Petronas Twin Towers in . 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 , or rolled near a target (see ). 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 or a , or aim an object into the earth such as a . 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 , , , and were used to communicate information over greater distances. In more recent years, and cell phone towers facilitate communication by expanding the range of the transmitter. The 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 bridges 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.

are used to give visibility to help direct aviation traffic.


Other

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

See also

General


Warfare


Further reading
  • Fritz Leonhardt (1989), Towers: a historical survey, Butterworth Architecture, 343 pages.


External links
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