Leaning edge technology in Italy and Britain

The Leaning Tower of Pisa was reopened to the public this week eight years ago, following a decade of reconstruction and safety work that engineers declared would make it stable for at least another 300 years.

The work included removing heavy bells and excavating soil from underneath the raised end, straightening the tower by 45cm and returning it to the exact position it occupied in 1838.

La Torre di Pisa is a freestanding bell tower of the cathedral of Pisa that was built in three stages, over a period of around 177 years. It began leaning due to a poorly laid foundation and loose substrate five years into the build, in 1178, after construction had reached the third floor.

Work was subsequently halted for almost a century because the Pisans were at war with Genoa, Lucca and Florence. If the underlying soil had not been allowed to settle during this time the tower would almost certainly have toppled.

When construction resumed in 1272, engineers built upper floors with one side taller than the other to compensate for the tilt. This created a curve in the tower. Building was again halted in 1284, when the Pisans were defeated by the Genoans in the Battle of Meloria. The seventh floor was finally completed in 1319.

Following the removal of more earth from under the tower in 2008, engineers declared that the tower had stopped moving for the first time in its history. The tower has now lost its status as the world’s most lopsided building to a church steeple in the German village of Suurhusen.

The ‘Guinness book of records’ measured the angle of the German steeple at 5.19 degrees, compared with the leaning tower’s 3.97 degrees.

Readers interested in leaning buildings can get their fill without leaving Britain. The south-east tower of Caerphilly Castle, Mid Glamorgan, leans following Oliver Cromwell’s attempt at slighting after the English Civil War. And the original section of the Temple Church tower in Bristol leans westward because it was built on marshy land (but sections added following restoration work lean in the opposite direction). In King’s Lynn, the 13th century hexagonal Greyfriars Tower has a small but noticeable lean of just over one degree.

The Church of St Mary and All Saints in Chesterfield has become known as “the church of the crooked spire”. The twist of the wooden spire is by design, but the lean is due to a number of factors, including the use of unseasoned timber, the lack of skilled craftsmen (due to the black death) and the absence of cross bracing.