Jul 12, 2011

7 Wonders of the Medieval World - Part VII

Leaning Tower of Pisa

The Leaning Tower of Pisa (Torre pendente di Pisa) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa. It stands behind the Cathedral and is the third structure in Pisa's Campo dei Miracoli (field of miracles).

The leaning tower of Pisa leans by accident, not by design—yet it was constructed in such a way that it has resisted the pull of gravity. There is an unusual beauty and elegance to the tower, too, so much so that even were it not a leaning tower, it would attract attention as a cultural artifact.

The tower is constructed of white marble and has eight stories, including the chamber for the bells. The bottom story consists of 15 marble arches. Each of the next six stories contains 30 arches that surround the tower. The final story, the bell chamber itself, has 16 arches. There is a 294 step spiral staircase inside the tower leading to the top.

Cylindrical in shape, it is supplied with six open galleries. A cornice separates these galleries one from the other and each presents a series of small arches fitted on the capitals of the slender columns. In the base there is a series of big blind arcades with geometrical decorations. In the belfry there is the same design of arcades as that of the base.

Work on the ground floor began on August 8, 1173, during a period of military success and prosperity. This first floor is a blind arcade surrounded by pillars with classical Corinthian capitals, leaning against blind arches.

The tower began to sink after construction had progressed to the second floor in 1178. This was due to a meagre three-metre foundation, set in weak, unstable subsoil, a design that was flawed from the beginning. Construction was subsequently halted for almost a century, because the Republic of Pisa was almost continually engaged in battles with Genoa, Lucca and Florence. This allowed time for the underlying soil to settle.

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. 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 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.

From the ground on the lowest side the height of the tower is 55.86 meters (183.27 feet) and 56.70 meters (186.02 feet) on the highest side. The width of the walls at the base is 4.09 meters (13.42 feet) and at the top 2.48 meters (8.14 feet). Its weight is estimated at 14,500 tons.

Over the years various attempts have made to straighten the tower, including the injection of cement into the foundations and various types of bracing, but in the late 20th century the structure was still subsiding at the rate of 0.05 inches (1.2 mm) per year and in serious danger of collapse.

On January 7, 1990, after over two decades of stabilisation studies, the tower was closed to the public. 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 meters (50 cubic yards) of soil from underneath the raised end. The tower was straightened by 45 centimeters (18 inches), returning to its 1838 position. After a decade of corrective reconstruction and stabilization efforts, the tower was reopened to the public on December 15, 2001, and was declared stable for at least another 300 years.


Trisha said...

I saw this thing in 1998, before it was declared stable again :)

C R Ward said...

Even though you didn't get to go inside, I still envy you being able to see it in person!