The Little Tower That Could

The world of architecture has produced its share of epic failures.  From collapsing bridges to buildings that simply cave in, history records many such disastrous architectural failures.

A wonderful example of an epic fail in the world of engineering is the Leaning Tower of Pisa.  However, the Leaning Tower perhaps can be considered a mini failure as, although it is leaning precariously out of plumb, it has yet to succumb completely to gravity. 

And more than 800 years after the first stone was laid, that’s quite a feat.

Etching of Tower of Pisa near cathedralCredit: Webster's Millenium 2000

Towers feature prominently in the history of humanity.  In antiquity they functioned as outposts, lighthouses, and religious temples.  Almost all served a useful purpose.  Minaret towers, for example, in the ancient Islamic world were open-topped structures in which corpses were placed, away from the living, to have their bones picked clean by vultures.  The remains were then gathered up by the family and maintained as honored relics.

ziggurat at Ur (ancient Babylon, now Iraq)Credit: Britannica, 1998

Towers feature in many legends.  An early mention in literature is of the mythical Tower of Babel, the structure meant to take humans closer to their god.  This fictional structure was based on a very real edifice, a ziggurat (a graduated, stepped structure similar to the Aztec pyramids) known in ancient Babylonia as the Temple of Marduk (a Babylonian god).  Ziggurats pre-date tower building by several centuries.  Improvements in construction techniques and building materials paved the way for self-supporting towers.

The Bells…The Bells
Most towers were defensive, providing look-out vantage points and strategic defense positions for the besieged.  When the Catholic Church instituted its early program of monumental architecture, cathedrals with tall bell towers featured prominently on a city-scape or country village hillside.  These bell towers also served as sentry posts as needed. 

Bell towers have a long and rich architectural as well as artistic history.  Bell towers stood near churches, in public squares, and near palaces.  The towers, although occasionally attached to a host structure, were generally stand-alone units. Their function was communication – the bells tolled the hours of the day, they were used as warning systems, and they called the villagers to worship.  The towers of necessity needed to be taller than their surroundings for the bell tones to ring true and clear across the countryside.

In Italy, bell towers were called campaniles.  The earliest of these were purely functional.  They were unadorned, rounded structures capped with open arches on a platform. This amplified the bell’s sound.  After about the 10th Century AD, the Italians created more decorative towers.  The basic structures were modified into more visually pleasing square-shapes.  Early towers were made of sun-baked and oven-fired brick.  In Rome and Lombardy these rustic building blocks were displaced in favor of more elegant materials such as marble. 

The earliest campaniles usually had pyramidal roofs.  These were supplanted later with flat roofs adorned by castellated stonework and steeples.  A tower’s decorative features became prominent.  The Lombardy faction of campanile builders also expressed a greater aesthetic preference for accentuating the vertical lines of their towers, giving the illusion of sleekness and greater height. Pilasters (vertical columns) were added to give the effect of greater height, and the towers mid sections began to feature arches and stone cornices. 

Falling Down
In the great tradition of Italian campanile designers of its day, the Tower of Pisa was conceived as an aesthetically appealing piece of art, monumental architecture, and function.  Its plans devised an eight-story circular tower with decorative works that was meant to stand 185 feet tall.  It was the third and final structure of Pisa’s cathedral complex.   

The Tower’s construction was problematic; the ground selected for its building site was unstable, although this was not discovered until much later.  The construction on the project began in 1173Galileo GalileiCredit: Webster's Millenium 2000 AD.  The first three stories were completed and then work stopped on the project (funding, politics, etc.).  The Tower sat with no real progress for a century.  When work resumed in 1298 the builders discovered signs of shifting – the work that had been completed was slanting.  Rather than dismantle and start again, the engineers and builders shored up the ground with detritus, and continued building upward.  They made minor adjustments in the Tower’s first few stories (increasing the height of the arches on one side slightly to help level the stories above).

It was finished in 1372, but the Tower was doomed.  It continued to slant more dangerously, yet never toppled.  During Galileo’s day the Tower had already become a tourist attraction – it was considered miraculous it still stood at its precarious angle. [As for Galileo’s famous experiment (dropping two different weight cannonballs from the Tower’s top deck to prove objects of different weights fall at the same rate) it never happened.  Galileo had no need to do this – he already had worked out the problem mathematically and knew the results.  His actual confirmation experiment of what he already knew was gained by rolling balls down inclined planes.  Others later performed the Tower of Pisa version of the experiment and attributed it to Galileo]. 

The Tower continued to settle, both sinking into the ground on one side and leaning.  Discussions about what to do with it, (it was actually in danger of becoming a public menace as it could collapseLeaning Tower of Pisa (declination)Credit: Bill G. Chambers, 2011 on nearby structures) ranged from demolition to flying buttresses (arching external supports propped against it to shore it up).  There were even talks of cabling the Tower (looping lengths of rope around it and literally pulling it back into the vertical).

It was determined finally (and this probably was the best course of action) to leave the Tower roughly as it was.  Preservation efforts focused on stabilizing it; tons of concrete and fill were pumped into its base area to keep it from leaning further.  The Tower subsided at about 0.03 inches per year, and by 1990 it was out of plumb by almost 6 degrees – an astounding fifteen feet.  It was on the brink of collapse.  It was closed to the public as engineers implemented a project that shaved about 17 inches off the lean, reducing it to about 13.5 feet today.  The work was completed in May 2001; its current height is 166 feet and the leaning has stopped.

“Straighten Up!”
Although it is technically possible to realign the Tower of Pisa to true vertical it would prove disastrous.  During the entire balance of its construction after the leaning was first noted builders made adjustments to the structure as they went along.  Pulling the Tower upright would throw all that work “out of alignment” and would probably affect its structural integrity.

Rudimentary photo-manipulation skills are all that are needed to see why “straightening” the Leaning Tower of Pisa is a very bad idea indeed.  The attendant images will help visualize the issue:

"Straight" Tower of Pisa (showing adjustments)Credit: Bill G. Chambers, 2011

As seen in the upper left photo the Tower has been digitally brought into plumb.  It doesn’t look as if it is, though.  It looks more like a multi-tiered "Straight" Tower (w/ vertical and horizontal references)Credit: Bill G. Chambers, 2011wedding cake that is wobbly and shaky and sliding off to one side.  That's because it is.  The builders purposefully shifted their “leaning” floors slightly to the opposite side to help prevent further sliding and to at least make the building usable.  The optical illusion is only part illusion, however; the addition of the yellow rectangle helps make clear, in the second photo on the upper right, the Tower’s left hand edge is clearly vertical; the right hand edge displays the “sliding wedding cake” concave curve, however.  That’s what renders the structure sound while leaning, but would spell collapse if it were ever straightened.

In the end this epic fail (a bell tower that was unsafe and unstable, and frankly shouldn't still be “standing” or leaning) has come to charm millions around the world.  It is probably the thing for which Pisa, Italy, is best known (and for many it is probably the only thing known about Pisa).  The Leaning Tower of Pisa is a world-renowned icon, a testament to tenacity.  As campaniles go, it is the most famous; however, as a campanile (its intended purpose), it is an epic failure.

The Leaning Tower of Pisa (3 views, detail)Credit: Bill G. Chambers, 2011


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