Man’s Blunder, Nature’s Wonder

By Abigail Ronck ’05 and Leila Ledsinger ‘04

It’s purely mathematical, really.  The amount of money it originally cost to begin construction on a bell tower in Pisa: 60 coins.  The amount the tower earns each day from tourist ticket sales: over $60,000.  The endless wonder and mystery attributed to a stone building that bends like a willow in the wind: priceless.

Well, we think so anyway.  Priceless to indulge in a moment of aesthetic and intellectual wonder that animates and overwhelms us, while obscuring our ability to distinguish the real from the miraculous.   We can clearly see that the Leaning Tower of Pisa tilts…but it does not fall, inviting us to leave common sense behind and wonder how and why.  Perhaps the stone tower was accidentally tipped by the invisible hand of God, and continues to be held up by it. Or maybe its architect, riddled with insecurity and resentment after losing half a leg in an epic naval battle, designed the tower in accordance with his own stiltedness and unique line of sight, which rested a few degrees off center. It is possible that old school entrepreneurs intentionally designed the tower to lean, as a covert ploy to attract people from around the globe to witness its puzzling flaw.  Whatever we decide in those moments of wonder, the tower leaves each one of us privy to some sort of magnificence just beyond our grasp.  Priceless.

Although the tower inspires admiration for its human design, it is the tower’s natural flaw that summons an aura of spectacle and enigma. In 1172, the first foundational stones were laid in ground; they were composed of clay, fine sand, and shells. In addition to marking a cathedral, baptistery, and cemetery, the tower was constructed to demonstrate the considerable level of brilliance, wealth, and power reached by the thriving marine republic of Pisa. However, the stones were not all that was embedded in this marshy and unstable ground. The combination of subterranean water and other natural phenomena, an unusual construction history, and of course a sprinkling of destiny, would complete the recipe for an architectural “blunder”, bringing fame and millions of tourists to the otherwise quiet town of Pisa, Italy for the next 800 years.

It wasn’t until 1996 that experts in the field of soil mechanics synthesized their knowledge of the shifting water table beneath the tower’s surface to devise a method to confront this natural phenomenon while still preserving the architecture’s famous flaw.

Despite the brilliance of structural design, the tower’s crooked form became apparent after a mere five feet of its base had been completed. However, construction continued until 1178, by which time three of the tower’s eight stories had been erected.  Construction then halted for one hundred years to come, though the reasons for the hiatus remain unknown. Nonetheless, call it luck or perhaps even fate, this crucial rest period allowed the foundation soil to settle. Without the delay, the underlying soils would not have had time to consolidate and the already leaning tower would have inevitably toppled.

Construction recommenced in 1272, though the ground continued to shift and the tower continued to incline by a noticeable one degree, or 2.7 feet, to the south. By 1278, seven stories were completed, and over the next 90 years, the angle would increase to about 1.6 degrees. Perplexed workers building the bell tower believed that the incline was the result of a design flaw and tried to compensate by adding three extra steps to the tower’s south side bell chamber floor. However, the attempted correction not only failed to stop the tower’s progressive tilt, but also gave it a disfigured appearance, which caused its upper stories to look as though they were bending upwards. The tower was finally completed in 1370, and left for centuries to its slanting fate. Trembling at the mercy of the earth’s undulations, it seemed an ironic end to the ambitions of its designers, constructed to flaunt the precision and accomplishment of 12^th century Pisa.

Although it was “finished”, it was apparent by the early 1800’s that the tower was in need of a little human intervention. By this time, experts were finally able to pinpoint exactly why the tower was leaning. Constructed upon a surface of sandy, marshy soil, the tower’s slant had been caused by a water table discovered just below the earth’s surface. The water table fluctuates seasonally, forcing the tower’s foundation to rise and fall with the shifting soil. During the first century of the tower’s life, soil beneath its northern base caused it to lean slightly towards the north. Gradually, with changing weather, the tower shifted direction and angle, centered itself, and then began to lean towards the south, where it has steadily continued to slant for the past 700 years. We surmise that this stubborn affinity for the south reflects the tower’s preference for warmer temperatures, though experts argue that the tower was simply too settled to shift back again.

Constructed upon a surface of sandy, marshy soil, the tower’s slant had been caused by a water table discovered just below the earth’s surface.

Now that experts had solved the mystery with regard to why and when directional oscillations and angular increases occurred, they moved on to perhaps an even more crucial dilemma.  How could they combat the inevitable increase in the tower’s lean and prevent it from buckling?  Early attempts to halt movement included inserting eighty tons of a thin mortar called grout into the tower’s masonry foundation in an attempt to strengthen its base.  Failed.  In 1990, the tower was closed to the public for safety reasons, and measures were taken to stabilize it with an anchored cable system and lead counterweights, which succeeded in reducing, but not halting the lean.  Only a temporary fix.

Believe it or not, it wasn’t until 1996 that experts in the field of soil mechanics synthesized their knowledge of the shifting water table beneath the tower’s surface to devise a method to confront this natural phenomenon while still preserving the architecture’s famous flaw. With precise scientific calculations and approximately six million dollars, the scientists implemented a successful soil extraction method involving tubes that funnel soil out of the ground beneath the tower at a rate of five gallons per day.  Ultimately, when the process was complete, the ground cavity closed slowly and gently, causing the tower to right itself by almost an inch at its base—five times more than originally projected.  The Leaning Tower of Pisa was reopened to the public in 2001, straightened by 1.5 feet at its top and having gained 300 years to its upstanding life by returning to an inclination last seen in 1700.

After millions of man-hours and dollars spent to preserve a piece of faulty architecture, you probably want to ask: still priceless?  Well, we think so.  Perhaps now we understand, scientifically, why the Leaning Tower of Pisa leans, but the value of its aesthetic flaw and man’s many attempts to preserve it may forever remain incomprehensible.  Maybe its mysterious architect did have great foresight and intentionally began construction upon shifting soil to give it a unique flare.  Maybe God had a hand in it too, giving the tower a little character and an ability to persevere over all we humans can do to “fix” it. We take back what we said before—nothing can be purely mathematical.  After all, there can really be no calculations, no amount of money, or degree of perfection attached to the awesome moment of fusion between understanding and utter confusion, reality and unbridled imagination.  

Fast Facts

Official Name: Torre Pendente di Pisa
Location: Campo dei Miracoli (“Field of Miracles”)
Years Built: 1173-1350
Times Construction Was Stopped Due to War: 3
Height: 185 feet
Thickness of Walls at the Base: 8 feet
Total number of Bells in tower: 7, tuned to the note of the musical scale
Weight of the Largest Bell: 3.5 tons
Greatest Lean: 15.6 feet (1997)