Page 99 - How It Works - Book of Amazing Answers To Curious Questions, 12

Historye ----------Q�

Wh y does The Bell chamber was
Bell tower
added in 1372. It
features seven bells -
the Tower of largest of which was
one for each note of the
musical scale. The
installed in 1655.
Pisa lean? Shape
The tower has a
cylindrical body
Find out how the tower was encircled with arches
and columns. The
made and how it went wrong ... hollow shell which
central body is a
features an external
he local architects and city officials designed the wall of white and
grey limestone.
complex at Piazza dei Miracoli (the Square of
T Miracles) as a dedication to art, and as such it is
thought the principles of science and engineering were Spiral staircase
not fully understood. The inner wall was
The tower was built in three stages over a period fashioned from worked
limestone and
stretching nearly two centuries. The first part of the tower
comprises a 296·step
was built during a time of town prosperity and as such spiral staircase.
heavy white marble was used for the base and tower, with
limestone used for the interior and exterior design features.
Disaster occurred just five years after work began, as the Curvature
In 1272 architects
workers finalised the interior of the third floor. The tower
fashioned a corrective
was sinking because the weight of the marble building axial inclination where
was too much for the extremely insufficient three-metre the walls on one side
of the tower were
foundations which had been set in weak and unstable taller than the other -
soil that contained a malleable mixture of clay, sand and giving the building its
concave appearance.
rubble. The construction was halted for nearly a century
to allow the soil to settle. In 1272 work recommenced as
engineers began to build the tower's middle section. To Third floor
compensate for the continuing problem of its lean, the
Upon reaching this level,
workers built one side of the wall taller than the other. engineers noticed the
Subsequently the tower began to lean in the opposite tower was starting to sink.
The heavy white marble
direction and caused it to curve. War caused a break in had become
construction and the seventh floor was not completed too heavy for the
until1319 and the eighth level, featuring the belfry, foundations set in soil.
was finally added in 1372.
The tower was built First floor interior
Lining the inside the first
floor is a series of arches in a
over a period stretchin typical Romanesque blind
arcade style, intersected
nearly two centuries classical Corinthian capitals.
with columns displaying
How does it not fa ll over
., Foundations
n 1964 a desperate Italian Government requested aid to stop the Made of white marble, the
Itower from toppling. One of the first methods to be tested was to construction began in 1173
add 800 tons of lead counterweights to the raised end of the base, during a time of prosperity in
but this only added to its subsidence. With the problem worsening Pisa thanks to the success
it was decided to close the tower in 1990 and remove the bells to of its military.
relieve some of the weight.
Cables were cinched around the third level and grounded several
hundred metres away to anchor the weight. Work began on
removing some 38 cubic tons of soil from under the raised end of
the base, which straightened the tower by 18 inches - regaining an
angle last recorded in 1838. Ten years of corrective stabilisation
followed and the tower reopened to the public in 2001. In 2008
another 70 tons of earth was excavated and for the first time the
structure has officially stopped moving.

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