Why does the Tower of Pisa lean to one side?
The world-famous Italian landmark attracts thousands of visitors each year – but why does it lean to one side? BBC History Revealed explains when it was built and explores the attempts that have been made to correct it through history…
Construction on the Tower of Pisa, which began in 1173, had reached only the third storey when architects noticed that the white-marble campanile (bell tower) was leaning.
The design was flawed from the start. Despite plans for the tower to be 56 metres high, the foundations were only three metres deep initially. To make matters worse, the soil was unstable (the name Pisa, after all, comes from the Greek for ‘marshy land’).
Before serious attempts could be made to correct it, war broke out between the Italian city states. Building was halted for over a century. The break, however, allowed the tower and its foundations to settle – without it, the tower would have probably collapsed.
The second phase of building commenced in 1272, and chief architect Giovanni di Simone attempted to correct the lean by making the next storey taller on the shorter side. This just made it heavier, which caused the tower to sink more. It wouldn’t be until the late-14th century that the tower was finally completed.
At its worst, the lean was 5.5 degrees. Between 1990–2001, a major project removed earth from the taller side, which reduced the lean to 3.97 degrees. It is thought the tower should now be stable for at least 200 years.