The Leaning Tower of Pisa leans because its shallow 3 m (10 ft) foundation rests on soft, unstable subsoil, a mix of clay, fine sand, and silt that cannot bear the tower's weight evenly. It started tilting during construction in the 1170s, after only three floors were built. Today it leans about 3.97 degrees.
The Leaning Tower of Pisa is recognized as one of the remarkable wonders of the medieval period. As its name suggests… it leans! It is the campanile, or freestanding bell tower, of Pisa Cathedral, a slender, eight-story cylinder of white marble standing about 56 m (183 ft) tall. Interestingly, the architects behind this unique, tilted structure never planned for it to lean. Their original goal was simply to build a straightforward bell tower. However, they had no idea that their seemingly simple project would eventually become a marvel that captivates people worldwide.
The Beginning Of The Tilt
Tall and heavy buildings rely heavily on their foundations. Construction began in 1173, but in the case of this tower the foundation was merely 3 m (10 ft) deep and was set on soft, unstable subsoil, a mix of clay, fine sand, and silt. This waterlogged ground compressed unevenly and proved incapable of supporting the massive weight of the tower, resulting in its distinctive lean. The tilt actually appeared while the tower was still going up: by the time the third floor was finished, around 1178, the structure had already begun to sink toward the south.
Upon noticing the tilt, construction was halted for nearly a century. Ironically, that long pause may have saved the tower. The break (forced in part by an ongoing war with Genoa, which directed the authorities' focus elsewhere) gave the soft soil beneath the structure decades to compress and settle, which is the only reason the foundation could later bear the weight of the upper floors.
Start And Stop Of Construction
In 1272, Giovanni di Simone resumed construction and added more floors. To counteract the tilt, he built the upper floors taller on the shorter (sinking) side than on the other. This is why the tower is not a straight cylinder but is slightly curved, almost banana-shaped, when you look closely. However, the extra masonry only added weight to the weak side, and the adjustment ended up exacerbating the lean even further.
Construction was halted again in 1284 because of the Battle of Meloria, a naval defeat by Genoa. By 1319, the seventh floor was completed, and the bell chamber that crowns the tower was finally added in 1372, nearly 200 years after the first stone was laid. The tower was subsequently left largely untouched until the 19th century. It is also the structure forever linked to Galileo Galilei, who supposedly dropped two balls of different weights from it to prove they fall at the same rate. Historians regard that story as apocryphal, an invention of Galileo's student and biographer Vincenzo Viviani, with no support in Galileo's own writings.
During World War II, the tower narrowly escaped destruction by American troops, who had orders to demolish any structures that could provide cover for German snipers. Fortunately, the generals chose to spare the tower, leaving it unharmed. (Source)
The Resurrection
By 1990, the tower leaned about 5.5 degrees, and engineers feared it was close to toppling. Italy had sought outside help to stop the tower from collapsing as far back as 1964, with the firm condition that the famous tilt that draws tourists be preserved, not erased. As a stopgap, roughly 600 tonnes (about 660 US tons) of lead counterweights were stacked on the high (north) side to keep the tower from leaning further while a permanent fix was worked out.
In 1990, the Leaning Tower was closed to the public. The bells were taken down, and an international committee of engineers and historians took charge of the rescue. Their clever solution, carried out between 1993 and 2001, was a technique called soil extraction: drilling angled bores under the raised north side and carefully scooping out small amounts of soil, so that side settled and the tower gently rotated back toward vertical.
The tower reopened to the public in 2001. The work trimmed the lean from about 5.5 degrees to roughly 3.97 degrees (close to 4 degrees), pulling the top back by about 45 cm and leaving an overhang of around 4 m (13 ft) at the summit. Engineers announced in 2008 that the tower had stopped moving for the first time in its history and should remain stable for at least 200 years. So yes, it still leans, by design, and despite its notable tilt, the tower continues to stand tall.
Which Way Does The Leaning Tower Of Pisa Lean?
Here is a detail most photos quietly hide: the tower leans toward the south. That has been the case from the very start. When the foundation first began to settle unevenly during construction in the 1170s, the building sank on its south side, and that is still the direction it tips today. The famous tilt you see in every tourist snapshot is a lean to the south, away from the cathedral that sits just to its north.
And yes, it genuinely leans, this is no optical illusion or trick of the architecture. The tower stands about 55.86 m (183 ft) tall on its low (south) side and 56.67 m (186 ft) on its high (north) side, a gap you can measure precisely because one edge has sunk further into the ground than the other. After the rescue work of the 1990s, the tilt settled at roughly 3.97 degrees from vertical, which leaves the top of the tower hanging about 4 m (13 ft) out beyond its base. Climb the 294 marble steps of the internal spiral staircase (some counts say 296, depending on which side you tally), and you can actually feel the floor slope beneath your feet as you wind your way up.
Who Built The Leaning Tower Of Pisa, And Why?
The tower was never meant to be a standalone wonder. It is the campanile, the freestanding bell tower, of Pisa Cathedral, and it stands in the Piazza dei Miracoli (the "Square of Miracles"), sharing the green lawn with the cathedral, the round baptistery, and the Camposanto cemetery. Its whole job was to hold the cathedral's bells, and there are seven of them, one tuned to each note of the major musical scale. So the original purpose was thoroughly down-to-earth. The lean, the fame, and the millions of visitors all arrived later, entirely by accident.
So who actually designed it? Honestly, nobody is certain, and that is part of the tower's charm. The identity of the original architect is a real subject of debate among historians. For centuries, credit went to Bonanno Pisano, a 12th-century Pisan artist better known for his magnificent bronze cathedral doors. A fragment bearing his name was found at the foot of the tower in 1820, which fueled the attribution, though that piece may simply have belonged to one of his bronze works. More recent scholarship, including a 2001 study, points instead to Diotisalvi, the architect behind Pisa's baptistery and the bell tower of San Nicola, both of which share design features with the leaning campanile. Because construction dragged on for nearly two centuries, several master builders left their mark, which is why no single name can claim the whole tower. It is also the structure forever tied to Galileo and the idea that all objects fall at the same rate, although, as we saw earlier, that dropped-cannonballs experiment is almost certainly a legend.
