The tower of Pisa has been leaning so long. Try 840 years! So it’s just natural to assume it will defy gravity forever. However the famous structure has been in danger of collapsing almost since its first brick was laid.
It began leaning shortly after construction started in 1173. Builders had only reached just the third of the tower’s planned eight stories when its foundation began to settle unevenly on soft soil that is composed of mud, sand and clay. As a result, the structure slightly listed to the north. Laborers tried to repair this by making the columns and arches of the third story on the sinking northern side slightly taller. However political unrest halted construction.
The tower sat unfinished for nearly a century, but it was not done moving. By the time work resumed in 1272, the tower tilted to the south (which is the direction it still leans today)
The rate of incline was sharpest during the 14th century, although this did not stop town officials or the tower designers from moving forward with construction. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean by angling the eighth story, with its bell chamber, northward.
None of these measures succeeded, and slowly, over the years, the structure reached an incline of 5.5 degrees. Then, in 1989, a similarly constructed bell tower located in Pavia, northern Italy, collapsed suddenly.
Officials became worried the tower of Pisa would suffer a similar fate so they rallied together an international team to see if the tower could be brought back from the brink.
By 2001, the team had decreased the tower’s lean by 44 centimeters (17 inches), enough to make officials confident that they could reopen the monument to the public.
In spite of these potential problems, engineers expect the famous structure will remain stable for at least another 200 years. By then, another intervention may be required, but the technology available to make improvements could be far more advanced and preserve the tower for another 800 years.