Why the leaning tower of Venice is leaning?

Answer 1

it got its name because it is a leaning tower and it was built in a city in Italy called pisa
The Leaning Tower of Pisa is actually simply Campanile di Santa Maria or Campanile del Duomo ("belltower of St.Mary" or "belltower of the Cathedral") being the church dedicated to the Assumption of St.Mary.

After the florentine occupation of the city, nearly all the towers were destroyed and this was one of the few that remained. It was so beautiful and well-knowed that it was THE tower of the city of Pisa par excellence.

Nowadays everybody refer it simply as "The tower of Pisa" or "The leaning tower", but it is not a name.

The real name can be found on a XII century document were it is talked about the Operae campanilis petrarum sancte Mariethat means the "Work of the stones of the belltower of St.Mary".

The tower began to sink after construction had progressed to the third floor in 1178. This was due to a mere three-metre foundation, set in weak, unstable subsoil, a design that was flawed from the beginning. Construction was subsequently halted for almost a century, because the Republic of Pisa was almost continually engaged in battles with Genoa, Lucca and Florence.

This allowed time for the underlying soil to settle. Otherwise, the tower would almost certainly have toppled. In 1198 clocks were temporarily installed on the third floor of the unfinished construction.

In 1272 construction resumed under Giovanni di Simone, supposed architect of the Camposanto. In an effort to compensate for the tilt, the engineers built upper floors with one side taller than the other. Because of this, the tower is actually curved. Construction was halted again in 1284 because of a war, but continued some years later and laster between 1360 and 1370 maybe by Tommaso Pisano.

Answer 2

They realized it was starting to tilt early on and tried to correct.

Answer 3

The tower began leaning during construction. It was built on soft soil (clay, sand and mud). The foundation began to settle and the building began to list towards the north.