About the Tower of Pisa

The Leaning Tower of Pisa is an iconic monument, due entirely to its long-standing and unintended tilt. However, the tower and its white marble make for a lovely example of medieval Italian architecture, and a marvelous attraction its own right. The tower and its slouching posture have enjoyed a long history, including recent action taken to prevent the tower from collapsing.

Pisa

Pisa is a Tuscan city, located at the mouth of the Arno and downriver from Florence. Pisa's fortunes rose in the 11th century, as the city and its republic became one of the most important maritime states in Italy. It was during the 12th century that Pisa reached its zenith, and construction on the Tower of Pisa began. However, Pisa's prominence blocked the aspirations of Florence, Lucca, Massa and Volterra, and made it a major rival of Genoa. In the late 13th century, the Pisan navy lost of the Battle of Meloria, a setback from which the Republic of Pisa never recovered. By that time, the famous tower had six floors, with the seventh and eighth being added during Pisa's twilight years.

History

Ground was broken on the Tower in August, 1173, but it would not be finished for 177 years. Construction on the tower moved in fits and starts, and is usually described as having proceeded in three stages. The first push built the tower up to three floors, but by then, the building was already starting to sink, and the Pisans were distracted by a succession of foreign wars. Construction was not resumed until 1272. The new architect attempted to compensate for the Tower's sinking and tilt by building the new floors with one side higher than the other. The result is that the Tower is actually slightly curved, and also that the weight differential caused the tower to begin shifting away from its original tilt and to its present one. This stage came to a halt in 1284, after the Pisans lost at Meloria. The seventh floor was added in 1317, and the bell chamber in 1372.

Dimensions

The Leaning Tower of Pisa is 183.27 feet tall at its lowest and 186.02 feet tall at its highest. The walls are 13.42 feet thick at the base, and 8.14 feet thick at the top. There are two staircases, with 296 and 294 steps. The lesser staircase is on the lower side of the tower, and needs two fewer steps to reach the top.

The Leaning

The tower leans because it was built on a shifty, weak substrate and only had a foundation of about eight feet. Sound building technique requires a heavy structure like the Tower of Pisa (it weighs 16,000 tons) to be firmly anchored to bedrock. The result was that the soil that the tower was built on shifted and settled, producing a 5.5 degree tilt. The recent rescue effort to prevent the tower from falling over pulled it to a 3.99 degree tilt.

The Rescue

Between 1990 and 2008, efforts were made to stabilize the tower, which had been slowly but steadily tilting ever lower and was in danger of eventual collapse. The area around the foundation was excavated and then anchored with massive lead weights. The tower is now said to be stable, and is predicted to remain so for at least two centuries.

Mythology

It is believed that the tower was used by Galileo for his experiments with gravity. As the story goes, he dropped two cannonballs of different weight from the top to show that their speed was not a result of their mass. However, the sole source of this tale is Galileo's secretary, and there is some doubt as to its veracity.