The so-called Leaning Tower of Pisa, built in 1173 for the Italian town of Pisa, is known around the world for its infamous leaning slant, attracting tourists throughout the year. But leaning was never part of the building’s original plan; in fact, the Italian architects and engineers did everything they could to try and halt and correct the tower’s slanted profile, some of which inadvertently made the building lean even more. Despite its precarious appearance, the building has evaded collapse over the centuries and has gone on to become one of the most celebrated architectural marvels in the world. But why does it actually lean, and how has it remained standing? We take a closer look at the story behind this fascinating bell tower.
The Leaning Tower of Pisa Was Built on Unstable Soil
The Leaning Tower of Pisa was built on alluvial soil made up of sand, clay and shells. This substance was particularly soft and unable to withstand heavy loads, making it far from the ideal location to construct an eight-storey bell tower. Nonetheless, the building plans for a bell tower situated in the cathedral complex of Pisa went ahead.
It Began Its Life as a Straight Tower
Amazingly the tower so famous for its slanted lean actually began its life as a straight tower. Workers were able to successfully build the first three layers of the tower before they noticed that its foundations were settling and sinking unevenly in the soil, causing it to gradually begin leaning. Building work halted as engineers went back to the drawing table to look for a solution that would allow them to complete the building in its eight-storey entirety.
A War Between Pisa and Genoa Broke Out
Get the latest articles delivered to your inbox
Sign up to our Free Weekly Newsletter
Meanwhile a war broke out between Pisa and Genoa, which led to a significant delay in the building’s progress, lasting nearly 100 years. During this time the tower’s foundations settled further into the soil, and it is perhaps because of this settling period that the building was able to remain securely rooted in the ground. This period of ‘settling in’ may well have allowed the building’s foundations to withstand the weight of the additional levels once construction work finally began again.
Construction Plans Changed
Building work on the tower resumed under the leadership of engineer Giovanni di Simone, whose plan was to add in additional masonry on the building’s shorter side in order to compensate for its uneven appearance. However, the extra weight only worsened the building’s problem, causing it to sink deeper into the ground and eventually tilt even more. In spite of these issues, the building’s construction was finally completed in 1370. The tower continued to gradually lean at a rate of around 0.05 inches every year following its completion, giving it the quirky appearance that has made it so famous.
It Has a Southward Lean
Aerial photos reveal the leaning Tower of Pisa leans in a south-southeast direction, which has played a part in helping it remain standing. The hot Italian sun hits the south side of the tower, which is shorter, causing its height to increase and thereby temporarily decreasing the angle of its tilt. If the tower had been built facing the opposite direction, its fate may well have been entirely different.
Will the Leaning Tower of Pisa Fall?
In 1990, the tower reached a dangerous lean of 5.5 degrees from its perpendicular, leading to extensive restoration work. Engineers were able to remove soil from beneath the tower and add counterweights where needed, correcting the lean by 1.5 degrees. Following extensive testing in 2008, evidence suggests the tower has stopped sinking and is now in a stable position. Experts agree that the tower will not fall for another 200 years at least, barring any natural or man-made disasters.
