9 August: Leaning Tower of Pisa

On this date in 1173, the foundations of the Tower of Pisa were laid.  Here are ten things you might not know about the Leaning Tower:

1. It's a bell tower, a freestanding one, of the Cathedral of Pisa. It has seven bells, one for each note of the musical scale.
2. One of the bells is older than the tower itself. That is the fifth bell or the Pasquareccia, so named because it was rung on Easter Day. The bell came from the tower Vergata in Palazzo Pretorio in Pisa, where it was called La Giustizia (The Justice), and was tolled to announce executions of criminals and traitors, such as Count Ugolino in 1289. It was moved to the Pisa Tower when its original Pasquareccia broke.
3. It took 199 years to build, although to be fair to the builders, construction was halted several times because of wars.
4. It leans because the architects and builders failed to realise the ground in Pisa was too unstable to support the proposed tower. Also because they only built a three foot foundation for a tower that was to be over 180 feet tall. The name Pisa comes from the Greek for "marshy land". You'd have thought that would have given them a clue.
5. It started to lean in 1178, before they'd even finished building it. It owes its continued existence to the first century long halt in construction, because that allowed the ground beneath it to settle before more stories were piled on. Without that break, the tower would have fallen over long ago.
6. The tower is actually curved, because the second generation of builders and engineers, led by Giovanni di Simone, architect of the Camposanto, attempted to compensate for the tilt by building the floors with one side higher than the other. Hence the two spiral staircases inside have different numbers of steps. One has 294, the other has 296. The efforts to correct the tilt at this time had the effect of changing the centre of gravity of the building which meant the lean actually switched direction from north to south.
7. In 1934, Italian dictator Benito Mussolini decided the leaning tower had to be corrected because it wasn't perfect and everything in Italy had to be perfect. Concrete and grout was pumped into the foundations, but all Mussolini actually achieved was to make the lean even worse. Between 1990 and 2001, extensive restoration work was carried out by modern engineers, led by one John Burland, who said that soil mechanics, the branch of engineering required to complete the task, had been his worst subject as an undergraduate. Presumably he got the hang of it in the end, as, following the restoration, the tilt was reduced from 5.5 degrees to 3.99, and the tower has been declared safe for another 200 years.
8. The tower was almost destroyed during the second world war. The Germans were using it as a lookout post, and the Americans, led by sergeant Leon Weckstein, arrived to carry out an artillery strike on it. Weckstein saw what a beautiful building it was, and didn't order the strike.
9. The story goes that Galileo Galilei once dropped two different sized cannonballs from the top of the tower to demonstrate that their speed of descent was independent of their mass. However, we don't know for sure that it happened, since there is only one account of it, by his follower and biographer Vincenzo Viviani, who probably wanted to big up his mentor's achievements. Modern scientists believe it was only a thought experiment of Galileo's and he never actually did it.
10. There are several other towers in Pisa which lean, thanks to the soft ground. San Nicola, a 12th century church located about half a mile south of the Leaning Tower of Pisa, leans slightly while San Michele degli Scalzi, an 11th century church about two miles east has a 5-degree tilt. There are other leaning buildings in other parts of the world, including one in Germany, the Leaning Tower of Suurhusen, which has a tilt of just 0.02 degrees less than Pisa's tower. The record for the most lop sided building goes to the Capital Gate building in Abu Dhabi, United Arab Emirates, with a tilt of 18 degrees, but it was intentionally built to be that way. Finally, there is a rock formation in Antarctica which is nicknamed “Tour de Pise” because it looks a bit like the Leaning Tower.