On August 9th 1173 work was begun at the cathedral at Pisa to lay the foundations for a bell tower. It would take 199 years to complete. The tower is seven stories high topped by a bell chamber. Five days later work began on the ground floor. In retrospect it might have been sensible to spend a little more time on the foundations. They are only three metres deep, which isn’t really enough for a building eight stories high. In addition to this the ground beneath the tower is soft. Seven metres of silt over a layer of clay which is softer on the south side of the tower. Again, unsuitable for a building that weighs around fourteen and a half thousand tonnes.
We can’t be certain who the original architect was. Perhaps they were keen to distance themselves from the project because in 1178, when work began on the second storey, the building had started to sink, first on the north side, then on the south. Then Pisa got involved in a lot of battles with neighbouring states and work on the tower ceased. Nothing was done for almost a hundred years and the tower settled some more.
The Pisans knew their tower was wonky but they kept going anyway. Work was resumed on the tower in 1272. In order to compensate for the lean, the architect (a different one, obviously) began to build using slightly larger stones on the south side of the tower in an attempt to rectify the problem. This means that the tower is slightly banana shaped. In 1278 work stopped again because of another war. The builders had by then begun work of the seventh floor.
In 1319 the seventh floor was finished and yet another architect designed a bell tower for the top that also leant in the opposing direction. The bell tower was completed in 1372. The tower has gradually sunk further and further into the ground on it’s south side. In 1838 someone decided it would be a good idea to dig a trench so that everyone could see the portion that had disappeared underground properly. It wasn’t a good idea. Within a few days the top of the tower had tipped a further two feet. In 1934, Mussolini decided that the leaning tower was not a good image for his vision of a new Italy. He wanted to straighten it. Holes were drilled in the floor and eighty (or two hundred, I’m not sure) tonnes of concrete poured into the foundations. It only made the tower lean a bit more.
More recently, someone had the idea of digging out the foundations underneath the north side. This has allowed the tower to settle back a little and it should be good for another two or three hundred years. That’s if an earthquake doesn’t get it before then.