Why is the Leaning Tower of Pisa Tilted?

The History Behind the Tower's Construction

The Leaning Tower of Pisa is actually the bell tower of the Pisa Cathedral, located next to the Baptistry and cemetery of this religious complex. This complex, situated between the Arno and Serchio rivers in Tuscany, Italy, was built in 1173. At that time, as the city of Pisa became an important port for trade, the construction of this religious complex, which housed the Leaning Tower, completed its fame.

Architectural Secrets: Who Built the Tower?

Although the identity of the original architect of the Leaning Tower of Pisa remains unknown, most credible sources attribute the first part of the complex to Bonanno Pisano and Gherardo di Gherardo. The second phase of construction, starting in 1275, was led by Giovanni di Simone, while Tommaso Pisano was responsible for completing the tower.

The Cause of the Lean: A Tale from 1173

The tilt of the tower dates back to the early years of its construction, in 1173. However, the issue became noticeable when construction on the third floor of the tower began in 1178. It seemed that the soft ground had weakened the tower’s foundation, causing the building to tilt toward the south. Shortly after this event, the war between Pisa and Genoa, another Italian city, delayed the completion of the structure for a century. While this delay ultimately worked in favor of the tower, as the foundations had time to sink further into the ground and prevent the tower from collapsing in the future, it caused significant problems during the tower’s construction, which stretched over two centuries.

The Efforts to Correct the Tilt

When construction resumed, the chief engineer, Giovanni di Simone, attempted to correct the tower’s tilt by increasing the height on the leaning side. However, this additional weight caused the structure to sink even further. Experts believe the primary cause of the settlement was the foundation being built on soft ground, composed of clay and sand.

The Ongoing Tilt: A Problem That Spanned Centuries

The construction of the tower was officially completed in 1370, but its tilt continued for six centuries, becoming an inseparable part of the restoration efforts. Over 800 years, it became clear that this 55-meter tower had not only tilted but had also sunk into the ground by about one or two millimeters per year. Today, the Leaning Tower of Pisa is more than 5 meters shorter than it originally was. The tilt is now only 4 degrees, or 3.96 meters, compared to 5.5 degrees before attempts were made to correct it.

Restoration Success: The Tower Stabilized

Since the tower's completion, many architects and engineers have attempted to correct its tilt. These efforts have included adding grout to the base, pouring a concrete ring around the base of the tower, placing lead weights on the northern side of the structure, installing thick cables to the upper part of the tower, and removing soil from beneath the northern part of the tower. Finally, after removing more than 70 tons of soil in 2008, engineers declared that the tower had stabilized enough to stop moving. It is said that the Leaning Tower of Pisa should remain stable for the next 200 years.