Buzz
In 1172, Donna Berta di Bernardo gifted 60 silver coins to the local cathedral, intended for purchasing stones to form the base of a new bell tower.
Construction on the tower began the following year, but problems arose almost immediately. The foundation was laid on soft soil, consisting of clay, fine sand, and shells, as Pisa lies between the Arno and Serchio rivers. By the time the second floor was completed in 1178, the tower was already showing signs of leaning.
Construction was halted shortly thereafter for nearly a century, as Pisa engaged in wars with Genoa, Lucca, and Florence. This pause likely proved fortuitous, as modern analysis suggests the tower would have collapsed if building had continued without allowing time for the soil to settle.
When construction on the tower resumed, it was leaning 0.2 degrees to the north. By the time work began on the seventh floor, the tilt had shifted to one degree south. Construction then ceased once again for reasons that remain unclear.
DON'T LEAN ON ME
Over the following century, the tower's construction resumed sporadically.
The tower's tilt increased by another 1.6 degrees. To combat the lean, the builders made the southern side of the tower's remaining floors taller. However, the added weight caused the foundation to sink even further, exacerbating the lean. After completing all they could, the builders finished the tower in 1370.
Since its completion, engineers and architects from across the globe have closely monitored the tower’s lean and attempted various methods to correct it. These efforts have included injecting grout into the foundation, wrapping plastic-coated steel bands around the tower up to the second floor, constructing a concrete ring around its base, adding lead counterweights to the north side, installing anchored cables, and removing soil from beneath the north side.
Following the removal of over 70 metric tons of soil in 2008, engineers declared that the Leaning Tower of Pisa had finally been stabilized, halting its movement for the first time since construction began. The tower's lean now measures approximately four degrees (down from 5.5 degrees before restoration efforts), or roughly 13 feet past vertical. Experts believe the tower should remain stable for at least the next 200 years.
