The most photographed monument in Italy was never meant to lean - building on the vestiges of a sandy marshland gave the famous tower its perilous tilt.
The famous tower was intended to be a bell-tower for the collection of religious buildings in the centre of Pisa. A Cathedral, a Baptistry and a bell tower. Construction was started in 1173, it is thought under the direction of Diotisalvi - responsible also for other local buildings, like the bell tower on San Nicola and for the Baptistery. His name translates as "God save you" which seems quite apt, given what happened when the building reached the second floor.
Inadequate foundations meant that the tower start tilting early, and work was abandoned at the third floor because of fears the structure would collapse if they went any higher - and because Pisa entered into a long period of wars with Florence, Lucca and Genova.
In 1272 a new architect resumed building, and the century long period of settling had stabilised the foundations enough for him to progress. In an attempt to correct the lean, Giovanni di Simone, built one side of the tower higher than the other, effectively curving it. The tower was finally finished with a bell-chamber in 1372.
The curvature introduced by Giovanni di Simone however, rather than curing the tilt, made it worse and the tower continued to lean a little more every century.In 1990 the tower was closed to the public and was re-opened in 2008, finally stabilised. It had stopped moving for the first time in its history.