Eiffel Tower, Paris, France

The Eiffel Tower (French: Tour Eiffel) is an iron tower built on the Champ de Mars beside the River Seine in Paris. The tower has become a global icon of France and is one of the most recognizable structures in the world.

Introduction
The Parisian landmark is the tallest structure in Paris and one of the most recognized structures in the world and is named after its designer, engineer Gustave Eiffel. 6,719,200 people visited the tower in 2006 and more than 200,000,000 since its construction. This makes the tower the most visited paid monument in the world per year. Including the 24 m (79 ft) antenna, the structure is 324 m (1,063 ft) high (since 2000), which is equivalent to about 81 levels in a conventional building.

When the tower was completed in 1889 it replaced the Washington Monument as the world's tallest structure — a title it retained until 1930 when New York City's Chrysler Building (319 m — 1,047 ft tall) was completed. The tower is now the fifth-tallest structure in France and the tallest structure in Paris, with the second-tallest being the Tour Montparnasse (210 m — 689 ft), although that will soon be surpassed by Tour AXA (225.11 m — 738.36 ft).

The structure of the Eiffel Tower weighs 7,300 tons. Depending on the ambient temperature the top of the tower may shift away from the sun by up to 18 cm (7 in) due to thermal expansion of the metal on the side facing the sun. The tower also sways 6-7 cm (2-3 in) in the wind.

The first and second levels are accessible by stairs and lifts. A ticket booth at the south tower base sells tickets to use the stairs which begin at that location. At the first platform the stairs continue up from the east tower and the third level summit is only accessible by lift. Once you are on the first or second platform the stairs are open for anyone to ascend or descend regardless of whether you have purchased a lift ticket or stair ticket. The actual count of stairs includes 9 steps to the ticket booth at the base, 328 steps to the first level, 340 steps to the second level and 18 steps to the lift platform on the second level. When exiting the lift at the third level 15 more steps exist to ascend to the upper observation platform. The step count is printed periodically on the side of the stairs to give an indication of progress. The majority of the ascent allows for an unhindered view of the area directly beneath and around the tower except during brief stretches of the stairway that are enclosed.

Maintenance of the tower includes applying 50 to 60 tons of three graded tones of paint every seven years to protect it from rust. On occasion the colour of the paint is changed — the tower is currently painted a shade of brownish-grey. However, the tower is actually painted three different colours in order to make it look the same colour to an observer on the ground with the colors changing from dark to light from top to bottom. On the first floor there are interactive consoles hosting a poll for the colour to use for a future session of painting. The co-architects of the Eiffel Tower are Emile Nouguier, Maurice Koechlin and Stephen Sauvestre.

Background
The structure was built between 1887 and 1889 as the entrance arch for the Exposition Universelle, a World's Fair marking the centennial celebration of the French Revolution. Eiffel originally planned to build it in Canada, for the Universal Exposition of 1888, but they rejected it. The tower was inaugurated on 31 March 1889, and opened on 6 May. Three hundred workers joined together 18,038 pieces of puddled iron (a very pure form of structural iron), using two and a half million rivets, in a structural design by Maurice Koechlin. The risk of accident was great, for unlike modern skyscrapers the tower is an open frame without any intermediate floors except the two platforms. Yet because Eiffel took safety precautions including use of movable stagings, guard-rails and screens, only one man died.

The tower was met with resistance from the public when it was built, with many calling it an eyesore. (Novelist Guy de Maupassant — who claimed to hate the tower — supposedly ate lunch at the Tower's restaurant every day. When asked why, he answered that it was the one place in Paris where you couldn't see the Tower.) Today, it is widely considered to be a striking piece of structural art.

One of the great Hollywood movie clichés is that the view from a Parisian window always includes the tower. In reality, since zoning restrictions limit the height of most buildings in Paris to 7 stories, only the very few taller buildings have a clear view of the tower.

Eiffel had a permit for the tower to stand for 20 years, meaning it would have had to be dismantled in 1909, when its ownership would revert to the City of Paris. The City had planned to tear it down (part of the original contest rules for designing a tower was that it could be easily demolished) but as the tower proved valuable for communication purposes, it was allowed to remain after the expiration of the permit. The military used it to dispatch Parisian taxis to the front line during the First Battle of the Marne, and it therefore became a victory statue of that battle.

Shape of the tower
At the time the tower was built many people were shocked by its daring shape. Gustave Eiffel was criticised for the design and accused of trying to create something artistic, or inartistic according to the viewer, without regard to engineering. Eiffel and his engineers, as renowned bridge builders however, understood the importance of wind forces and knew that if they were going to build the tallest structure in the world they had to be certain it would withstand the wind.

The shape of the tower was therefore determined by mathematical calculation involving wind resistance. Several theories of this mathematical calculation have been proposed over the years, the most recent is a nonlinear integral differential equation based on counterbalancing the wind pressure on any point on the tower with the tension between the construction elements at that point. That shape is exponential.

Installations
Since the beginning of the 20th century, the tower has been used for radio transmission. Until the 1950s, an occasionally modified set of antenna wires ran from the summit to anchors on the Avenue de Suffren and Champ de Mars. They were connected to long-wave transmitters in small bunkers; in 1909, a permanent underground radio centre was built near the south pillar and still exists today. On 20 November 1913 the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained wireless signals with the United States Naval Observatory which used an antenna in Arlington, Virginia.

The object of the transmissions was to measure the difference in longitude between Paris and Washington, DC.

The tower has two restaurants: Altitude 95, on the first floor (95 m, 311 ft, above sea level); and the Jules Verne, an expensive gastronomical restaurant on the second floor, with a private lift. This restaurant has one star in the Michelin Red Guide. In January 2007 a new multi-Michelin star chef Alain Ducasse was brought in to run Jules Verne.

The uppermost observation deck, with a height of 275 metres, is the highest area of an architectural structure in the European Union open for the public.


The passenger lifts from ground level to the first level are operated by cables and pulleys driven by massive water-powered pistons. As they ascend the inclined arc of the legs, the elevator cabins tilt slightly, but with a slight jolt, every few seconds in order to keep the floor nearly level. The elevator works are on display and open to the public in a small museum located in one of the four tower bases, and waiting queues are much shorter than those for the tower ascent.