The Tower of Pisa is not celebrated for its immense size, as with the Great Wall of China or the Empire State Building. It is not celebrated for its spectacular beauty, as with the Taj Mahal or the Millau Viaduct. And it is not celebrated for its sense of ancient mystery, as with the Pyramids of Giza or Stonehenge. No, the Tower of Pisa, perhaps unique on my list, has an entirely different quality that has seen it capture the attention of the world: improbability. It seems to defy logic. Tilted southwards, it looks like it should fall down and, well, it really should have.
So what went wrong? The entire history of the Tower of Pisa is one of things being wrong and getting worse and worse. That it survives today is well against the odds. Work began in 1173 but didn't last very long - by 1178 and with three storeys built (of an eventual eight storeys), work halted for almost a century. The reason for this sudden and lengthy pause isn't really known, but it's reckoned the inclination was already showing. Imagine building three storeys over five years and then noticing it's sagging to one side... cause for concern. Work stopped to think things over, and the architect made his excuses and left - or was fired. We don't really know. Unlike the rest of the structures in the Piazza del Duomo, we have no idea about the Tower's architect: no inscription or epitaph was ever left with his name. Perhaps this was deliberate. And perhaps the long pause before construction resumed was deliberate - to let the tilting building set in the obviously unstable ground. As the 12th Century turned to the 13th Century, Pisa's fortunes declined after defeats in battle and loss of trade routes. Restarting a tilting tower wasn't the priority.
The Leaning Tower of Pisa was started in 1173 and has been falling over ever since. It was built as part of the Piazza del Duomo, or Cathedral Square, in Pisa, with three other larger religious buildings - a cathedral, a baptistry, and a kind of monumental cemetery - but was never meant to be the star of the show. It was simply supposed to be a pretty, but ultimately modest, bell tower, giving way to the much greater glory of the cathedral. Indeed, it is much smaller and aesthetically far simpler than the cathedral begun over a century earlier by an architect we know only as Buscheto. This 11th Century cathedral is roughly the size of the Hagia Sophia, with a marble facade, great bronze doors, and a lavish interior of carvings and columns; it should by rights be the pin-up boy of Pisa. No doubt Buscheto would be baffled to hear that the stupid, badly-designed tower built next to his masterpiece is now more acclaimed.
Work eventually recommenced in 1272, under a new architect, called Giovanni di Simone. At this point in medieval history, the Gothic Revolution was changing the way religious buildings were constructed, but he chose to continue the tower in the old-fashioned, heavier Romanesque style. He also recognised that something needed to be done about the lean. So from the 5th to the 7th storeys, he deliberately built a slant towards the north, to try and even things out. If you look very closely, you can see that the tower is actually curved. It was a nice idea, but his work was just as bulky and heavy as the first three storeys, adding even more weight onto the soft foundations. In 1278, just as he reached the top level of the belfry (that is, the chamber that holds the bells), work stopped again.
Again, the exact reasons are uncertain, but the ever-increasing lean seems the obvious candidate. Let the foundations settle, di Simone would have reckoned, and he had plenty of other work in the Piazza del Duomo to get on with. The stupid bell tower could wait. And wait it would have to do. Pisa went through more wars and more decline, including a crippling defeat to its rival, Genoa, in 1284. Its time as a power was over, although culturally it was still thriving. Work still continued on the Piazza, and although documentary evidence is imprecise, it seems the belfry was finally completed in around 1350 by a man called Tommaso d'Andrea. The tilt was so obvious by now that in another attempt to correct it, as we can see today, six steps were added up to the south side of the belfry floor but only four on the north side. With some finishing touches, by 1370, after almost two centuries, the Tower of Pisa was complete.
And with a lean of 1.6 degrees to the south. Nobody was very impressed. The Piazza del Duomo was supposed to be the pride of Pisa, and it had a stupid tower in it that looked like it was going to fall over. This was not a celebration of great architecture, it was the visible display of what happens when the guy in charge gets his sums wrong.
So why does it tilt? Quite simply, it's a fine balance between unstable soil, inadequate foundations, and a heavy stone building. At about 14,500 tonnes, 56 metres high, with just 3 metres of foundations, and ground that was once a bog, the weight and shape was enough to have the ground very, very slowly give way. If it was heavier, or the ground was softer, it would have toppled long ago. A lighter tower, or slightly harder ground may still have seen a tilt, but less dramatically so. Whoever started construction got their sums all wrong, but in a magically precise way to create a tower that was to spend centuries in the slow process of falling over.
It tilted 1.6 degrees in 1370, and by 1550 was at around 3.8 degrees. Measurements continued and in 1817 it was around 3.9 degrees, only a slight increase over the centuries. And so began a change in the Tower of Pisa's fortunes. The architects doing the 1817 measurements only had access as far back as 1550, and the difference in tilt was so negligible that it became widely thought that the Tower of Pisa had been deliberately built with a lean. Well, this changed everything. Suddenly, the Tower was so no longer an absurd, badly-conceived folly, it was a magnificent folly that people wanted to admire. The Pisans loved this - the Tower was no longer an embarrassment. The poet Shelly, his author wife Mary, and other famed writers and poets, including Lord Byron, settled in the area for a short while creating the "Pisa circle", further enhancing the appeal of the city. The 19th Century was a period in which a new-found appreciation for old buildings surfaced, and the quirkiness of the Leaning Tower of Pisa made it a big hit.
The tower's apparent stability was not to last, and it was largely to due to people not being able to take their hands off it. In 1838, an architect thought it a good idea to excavate around the base to liberate the parts of the tower that had sunk into the ground. Bad idea. This had the effect of subtly but seriously destabilising the Tower of Pisa all over again, by about 1cm a year. That may not sound a lot, but it equals a metre every century, and the real risk of sudden collapse. Numerous commissions were set up to try and figure out what to do - none of them came up with anything. In 1934, Mussolini approved the stupid idea of injecting over 90 tons of cement into the foundations, which had the dramatic consequence of further destabilising the tower, which lurched south-east, then north, then south, then east, then back to its original southern tilt (over a period of several months, I should add).
Then, in 1989, a different (non-tilted) 11th Century tower in the nearby city of Pavia suddenly collapsed, killing four people. Enough was enough. The Tower was Pisa had now surpassed the maximum tilt thought possible by computer simulations, and action had to be taken to fix it. It was closed down while a new commission was formed - the 17th such commission. External supports were put in place while a solution was worked out. Clearly, making the tower straight again would remove much of its appeal, but a safe tilt had to be found that wouldn't require visible supports. It took a decade to figure out, but by means of carefully calculated soil extraction the Tower of Pisa was "de-leaned" a little, back to its 1838 state, before people started messing with it. It was reopened to the public in late 2001.
Thus, the Leaning Tower of Pisa is no longer falling over, just leaning. It still looks joyously irregular, and gives a delightful photo opportunity for people pretending to hold it up.
I'd like to think I have more dignity than that, but I'm not promising anything. I expect to visit the Tower of Pisa in around spring of next year, and will give a fuller account of it and its history then, as well as my own impressions.