Leaning Tower of Pisa
Scientists have finally decoded the mystery behind how the Leaning Tower of Pisa still stands todayFranco Origlia/Getty Images

Soft soil and its interaction with the foundation of the Leaning Tower of Pisa give the heritage structure its signature lean. Surprisingly though, these are the same factors that have also kept it standing for over 500 years now.

Construction of the Tower began in 1173 and took about two centuries to complete. According to a report by Popular Science, a number of earthquakes have struck the region since. This comes as no surprise considering the fact that the region sits on several fault lines.

While it is difficult to track ancient earthquakes, the report mentions that there are records of quakes in this region since the time of the Romans. Earthquakes are believed to have played an important role in shaping the history of what is now modern-day Italy.

A new research conducted by a team from the University of Bristol revealed that there have been at least four major earthquakes in the region over the past centuries. But clearly, none of them have brought down the seemingly precarious tower in Pisa.

"Ironically, the very same soil that caused the leaning instability and brought the tower to the verge of collapse can be credited for helping it survive these seismic events," civil engineer George Mylonkanis, who was part of the study, said in the press release.

Researchers found that several factors have contributed in keeping the tower erect. The height of the tower, the soft ground, and stiffness of the construction - these factors ensure that when an earthquake hits the region, the vibrations do not have the same effect on the tower as they do on other constructions.

The report notes that the structure had not always stood at the angle that made it popular. In 1990, the structure started leaning a bit too dramatically for the safety of visitors. The landmark tower was closed to the public for a while.

It took a few months of work and engineering intervention to return the structure to its original 0.54 degree lean. The tower was anchored down to ensure it does not fall over.

The city of Pisa, known for its period architecture, has several other churches and a few more leaning towers, notes the report. Additionally, a few more examples of such precariously perched towers can be found in England as well.

In order to preserve the most famous one of them all, possibly, the use of sensors to constantly monitor the structure could prove to be one way to retain this heritage landmark in Italy. It could also help archaeologists preserve similar historic and heritage structures around the world.