Pisa

Yesterday I left Sestri-Levante to take the beautiful and very curvy road to La Spezia. It is through Cinque Terre (Wikipedia):

 

The Cinque Terre are five coastal villages in the province of La Spezia in the Liguria region of Italy. "Discovered" by foreigners in the late 20th century, they have come to be among the most popular areas of Italy among tourists. The coastline, the five villages, and the surrounding hillsides are all encapsulated in a national park by the same name. The Cinque Terre is a UNESCO World Heritage Site.

 

In the early afternoon I reached Pisa to visit the Tower of Pisa (Wikipedia):

The Leaning Tower of Pisa (Italian: Torre pendente di 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 it is the third structure in Pisa's Campo dei Miracoli (field of Miracles).

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 has allowed the foundation to shift direction.

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). Its weight is estimated at 14,500 tonnes. The tower has 294 steps. The tower leans at an angle of 5.5 degrees. This may not seem a lot, but this means that the tower is 4.5 metres from where it used to stand vertically.

Construction

The Tower of Pisa was a work of art, performed in three stages over a period of about 174 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 surrounded by pillars with classical capitals, leaning against blind arches.

The tower began to sink after construction progressed to the third floor. In an effort to compensate for the tilt, the engineers built higher floors with one side taller than the other. This made the tower begin lean in the other direction. Because of this, the tower is actually curved.^[2]

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 conditions with respect to wind and rain.^[3]

History

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. This is considered an apocryphal tale, and the only source for it comes from Galileo's secretary.^[4]

Benito Mussolini 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.^[5]

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.^[6]

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.^[7] A multinational task force of engineers, mathematicians and historians was assigned and met on the Azores islands to discuss stabilization methods. After over two decades of work 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 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.^[8] 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.^[8]

In 1987, the tower was declared as part of the Campo dei Miracoli UNESCO World Heritage Site along with neighbouring cathedral, baptistery and cemetery.