You have to see what a poorly projected work gives of itself! Indeed, that is definitely the famous Torre Pendente, a symbol of Bella Italia. More than once has been feared by the final collapse of the monument although, against all the laws of physics and with a little help from workers and some coincidences, there it is still standing ... and less inclined than ever. But, what do you think if we take a look at everything you need to know about the Tower of Pisa? 
1 - Twisted from the beginning
As we told you at the beginning, the leaning of the Tower of Pisa is due, in fact, to an error of the architect. There is some controversy about who was the architect who started it, in the second half of the 12th century. The truth is that just beginning the first part of the work, that monument began to deviate.
The reason seems to be more than clear. The tower was supported on a foundation of barely three meters deep and on top of that nobody took into account the quality of the terrain, which in Pisa is very swampy.
In fact Pisa was a "Repubblica Marinara", that is to say, one of the 4 naval powers of the Italian Middle Ages, thanks to its very well protected harbor in the estuary of the Arno River. But because of the remains that the river has been accumulating, the sea has moved more than 10 kilometers away. That makes the plain of Pisa and its surroundings very soft and very swampy ... and unfit to build very tall buildings.
So these engineers were so clever that they decided to build a tower on very shallow ground, so a landslide made the emblematic Tower of Pisa lean to the north when it was working on the third floor.
2 - Two centuries to finish it
Almost 180 years were spent, divided into three periods, to raise the Tower of Pisa. It is true that the project was stopped almost a century, due to the wars of principalities so fashionable in the Italy of those times. And luckily! some would say, because thanks to that lapse of time, the land could settle and that benefited the stability of the monument that, otherwise, would have hit the Tuscan terrain.
They returned to work, evidently with a new architect, in 1272. They raised another four floors but, taking care to vary the angle, to counteract the inclination they already had in the Romanesque arm. But again ... stop because of war!
It was necessary to wait another 100 years so that, finally, Andrea Pisano finished the bell tower. 
3 - Where the bell tolls
Few know that the Torre Pendente di Pisa is actually the bell tower of the city's cathedral, which is located in Piazza dei Miracoli. Formerly, when Romanesque art was in fashion in Italy, the bell tower and the baptistery used to be independent and separate from the cathedral (the Duomo of Florence also has it separate). The bell tower of the Duomo of Santa María Asunta, is equipped with seven bells and each of them corresponds with one of the seven musical notes. The largest of all was installed in the mid-seventeenth century and the tower, then, decided to turn to the other side, specifically to the south.
4 - Restorations and more restorations
We already mentioned that, from the beginning, the Tower of Pisa was an exercise in tightrope walking, in a desperate attempt to win the pulse of balance and the law of gravity. The interventions have not stopped at any time and some have had to be taken urgently, due to bad decisions that worsened the erection of the Pisan tower even more.
This is the case of what happened in the 19th century, when the architect Alessandro Della Gherardesca was restoring the monument. The famous man did not think of anything else than to draw a path so that the public could see the base of the bell tower. But to carry out his plans, he had to dig around the tower. Consequence? A flood and more inclination.
The situation has become desperate and dangerous on more than one occasion. But already in 1964, the Italian government was forced to ask for international help to try to tackle what seemed like the chronicle of an announced collapse. 
HERE I LEAVE THE LINK SO THAT THEY CAN HAVE THE COMPLETE INFORMATION. https://unitrips.es/todo-lo-que-necesitas-saber-sobre-la-torre-de-pisa/