The Leaning Tower of Pisa (Italian: Torre
pendente di Pisa) is the campanile, or
freestanding bell tower, of the cathedral. It is
situated behind the Cathedral. Although intended
to stand vertically, the tower began leaning to
the southeast soon after the onset of
construction in 1173 due to a poorly laid
foundation and loose substrate that had allowed
the foundation to shift.
The height of the tower is 55.86 metres (183.27
ft) on the lowest side and 56.70 metres (186.02
ft) on the highest side. The width of the walls
at the base is 4.09 metres (13.42 ft) and at the
top 2.48 metres (8.14 ft). Its weight is
estimated at 14,500 tonnes. The tower has 294
steps to the top.
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Construction was performed in three stages over a
period of about 174 years. Building of the first
floor began on August 9, 1173 during a period of
military success and prosperity. This first floor
is surrounded by pillars with classical capitals,
leaning against blind arches.
Galileo Galilei is said to have dropped two
cannon balls of different masses from the tower
to demonstrate that their descending speed was
independent of their mass. Many parts of the
story, however, are widely considered to be
merely legendary. While Galileo probably did
climb to the top of the tower and drop two items
to further prove his already-proven theory the
items were probably not two cannonballs.
Benito Mussolini in the 1930s ordered that the
tower be returned to a vertical position, so
concrete was poured into its foundation. However,
the result was that the tower actually sank
further into the soil.
During World War II, the Allies discovered that
the Nazis were using it as an observation post.
'A humble U.S. Army sergeant was briefly
entrusted with the fate of the tower. His
decision not to call in an artillery strike saved
the edifice.'
On 27 February 1964 the government of Italy
requested aid to prevent 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 formed and
later met in the Azores to discuss stabilization
methods. (right)

After over two decades of deliberation on the subject,
the tower was closed to the public in January
1990. 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.
After a further decade of corrective reconstruction and
stabilization efforts, the tower was reopened to
the public on December 15, 2001. It was found
that the lean was increasing due to the stonework
expanding and contracting each day due to the
heat of sunlight. This was working in combination
with the softer foundations on the lower
side.
Many methods were proposed to stabilize the
tower, including the addition of 800 metric tons
of lead counterweights to the raised end of the
base. The final solution to prevent the collapse
of the tower was to slightly straighten the tower
to a safer angle, by removing 38 m3 of soil from
underneath the raised end. The tower has been
declared stable for at least another 300 years.
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