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Tower of Pisa

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					Tower of Pisa
          The main information
• The Leaning Tower of Pisa or simply the Tower of
  Pisa (La Torre di Pisa) is the campanile, or freestanding
  bell tower, of the cathedral of the Italian city of Pisa. It is
  situated behind the Cathedral and is the third oldest
  structure in Pisa's Cathedral Square (Piazza del Duomo)
  after the Cathedral and the Baptistry.

• The height of the tower is 55.86 m (183.27 ft) from the
  ground on the lowest side and 56.70 m (186.02 ft) on the
  highest side. The width of the walls at the base is 4.09 m
  (13.42 ft) and at the top 2.48 m (8.14 ft). The tower has
  296 or 294 steps; the seventh floor has two fewer steps
  on the north-facing staircase.
                        Construction
•   The Tower of Pisa was a work of art, performed in three stages over a
    period of about 177 years. Construction of the first floor of the white marble
    campanile began on August 9, 1173, a period of military success and
    prosperity. This first floor is a blind arcade articulated by engaged columns
    with classical Corinthian capitals.
•   In 1272, construction resumed under Giovanni di Simone, architect of the
    Camposanto. In an effort to compensate for the tilt, the engineers built
    upper floors with one side taller than the other. This made the tower begin
    to lean in the other direction. Because of this, the tower is actually curved.
    Construction was halted again in 1284, when the Pisans were defeated by
    the Genoans in the Battle of Meloria.
•   The seventh floor was completed in 1319. The bell-chamber was not finally
    added until 1372. It was built by Tommaso di Andrea Pisano, who
    succeeded in harmonizing the Gothic elements of the bell-chamber with the
    Romanesque style of the tower. There are seven bells, one for each note of
    the musical major scale. The largest one was installed in 1655.
•   After a phase (1990-2001) of structural strengthening, the tower is currently
    undergoing gradual surface restoration, in order to repair visual damage,
    mostly corrosion and blackening. These are particularly strong due to the
    tower's age and to its particular exposure to wind and rain.
                              The architect
•   There has been controversy about
    the real identity of the architect of
    the Leaning Tower of Pisa. For
    many years, the design was
    attributed to Guglielmo and Bonanno
    Pisano, a well-known 12th-century
    resident artist of Pisa, famous for his
    bronze casting, particularly in the
    Pisa Duomo. Bonanno Pisano left
    Pisa in 1185 for Monreale, Sicily,
    only to come back and die in his
    home town. A piece of cast with his
    name was discovered at the foot of
    the tower in 1820, but this may be
    related to the bronze door in the
    façade of the cathedral that was
    destroyed in 1595. However recent
    studies seem to indicate Diotisalvi
    as the original architect due to the
    time of construction and affinity with
    other Diotisalvi works, notably the
    bell tower of San Nicola (Pisa) and
    the Baptistery in Pisa.
    History following construction

•   Galileo Galilei is said to have dropped two cannon balls of different masses
    from the tower to demonstrate that their speed of descent was independent
    of their mass. This is considered an apocryphal tale, its only source being
    however Galileo's secretary.
•   During World War II, the Allies discovered that the Nazis were using it as an
    observation post. A U.S. Army sergeant was briefly entrusted with the fate
    of the tower and his decision not to call in an artillery strike saved the tower
    from destruction.
•   On February 27, 1964, the government of Italy requested aid in preventing
    the tower from toppling. It was, however, considered important to retain the
    current tilt, due to the vital role that this element played in promoting the
    tourism industry of Pisa. A multinational task force of engineers,
    mathematicians and historians was assigned and met on the Azores islands
    to discuss stabilization methods. It was found that the tilt was increasing in
    combination with the softer foundations on the lower side. Many methods
    were proposed to stabilize the tower, including the addition of 800 metric
    tonnes of lead counterweights to the raised end of the base.
•   In 1987, the tower was declared as part of the Piazza del Duomo UNESCO
    World Heritage Site along with the neighbouring cathedral, baptistery and
    cemetery.
•   On January 7, 1990, after over
    two decades of work on the
    subject, the tower was closed to
    the public. While the tower was
    closed, the bells were removed to
    relieve some weight, and cables
    were cinched around the third
    level and anchored several
    hundred meters away. Apartments
    and houses in the path of the
    tower were vacated for safety. The
    final solution to prevent the
    collapse of the tower was to
    slightly straighten the tower to a
    safer angle, by removing 38 cubic
    metres (50 cu yd) of soil from
    underneath the raised end. The
    tower was straightened by
    18 inches (45 centimetres),
    returning to the exact position that
    it occupied in 1838. After a
    decade of corrective
    reconstruction and stabilization
    efforts, the tower was reopened to
    the public on December 15, 2001,
    and has been declared stable for
    at least another 300 years.

				
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