<![CDATA[Dome above Santa Maria del Fiore in Florence, Italy - Blog]]>Sat, 09 Dec 2017 07:19:08 -0800Weebly<![CDATA[A WRITER'S NOTE]]>Wed, 03 Aug 2011 12:14:27 GMThttp://florencedome.com/blog/a-writers-note1<![CDATA[A WRITER'S NOTE]]>Wed, 03 Aug 2011 12:14:23 GMThttp://florencedome.com/blog/a-writers-noteA WRITER’S NOTE

My name is George Lafferty and I’m an architect in the Kansas City area.  I was fortunate to have spent a year during college studying in Italy and get back whenever possible.  It was tremendously enjoyable to research, write, and illustrate this blog.

At times I wonder about my fascination with this dome.  Recently it occurred to me that perhaps the dome serves as a metaphor to the lives and experiences we all face.  Like the gaping, unfinished opening the Florentines saw at the top of their cathedral in 1420, each of us encounters an enormous project involving a large opening within us that needs to be constructed, and like the Florentines it is not a hole of our making.  In each of us the problems encountered in enclosing it are unique…there are no reliable plans or blueprints available to us.  Family and friends can guide us in the construction, but ultimately the work is our own, brick by brick.  We cannot live inside someone else’s dome.

The solutions developed to build the Florence Dome were intricate; it required an elaborate mixture of sandstone, marble, bricks, iron and wood to create the structural elements needed to make it stand.  In addition there were multiple inventions and innovations needed to assemble these elements.  Our personal domes aren’t structural, but they are intricate.  They require mixtures of thought, sacrifice, faith, discipline and creativity to make them stable. 

We have all seen people with their domes unfinished or poorly built.  Some domes collapse catastrophically, others deteriorate slowly and crumble over time.  The personal domes that endure are remarkable and often take a lifetime of work to assemble and maintain.

The dome in Florence has withstood three major earthquakes, numerous floods, high winds and violent storms, yet it stands firm almost 600 years later.  Likewise we face a multitude of incidents in the course of our lives that try to undermine or shatter our personal domes.  It requires constant diligence to keep them stable. 

Ultimately people are so much more fascinating than any structure regardless of what went into its design and construction, but I still find the metaphor applicable.  And while our domes may not last forever like the Florence dome, who knows…maybe they do. 

I discovered the poem below that sums it up very well:

THE BUILDERS(excerpt)

By Henry Wadsworth Longfellow (1807-1882)

All are architects of Fate,

      Working in these walls of Time;

Some with massive deeds and great,

      Some with ornaments of rhyme.

Nothing useless is, or low;

      Each thing in its place is best;

And what seems but idle show

      Strengthens and supports the rest.

For the structure that we raise,

      Time is with materials filled;

Our todays and yesterdays

      Are the blocks with which we build.

Truly shape and fashion these;

      Leave no yawning gaps between;

Think not, because no one sees;

      Such things will remain unseen.

In the elder days of Art,

      Builders wrought with greatest care

Each minute and unseen part;

      For the gods see everywhere.

Let us do our work as well,

      Both the seen and unseen;

Make the house where gods may dwell

      Beautiful, entire, and clean.

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Thank you.

 

If you are interested in knowing more about the dome at Santa Maria del Fiore please look for the following publications:

KING, ROSS.  Brunelleschi’s Dome.  London: Penguin Books, 2000.  This is a very well-written and comprehensive account of the Brunelleschi’s life and the construction of the dome.

PRAGER, FRANK D. & SCAGLIA, GUSTINA.  Brunelleschi, Studies of His Technologies and Inventions.  Cambridge, MA: The Massachusetts Institute of Technology, 1970.  This book is an in depth study of Brunelleschi’s inventions and technological innovations regarding the dome and other projects.

VASARI, GEORGIO.  Lives of the Artists.  Translated by George Bull.  Harmondsworth, England: Penguin Books, 1987.  This book was written in the 16th Century and contains many accounts of Brunelleschi’s life and achievements along with several other prominent artist from the time.

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<![CDATA[CONCLUSION]]>Fri, 01 Jul 2011 13:29:58 GMThttp://florencedome.com/blog/concusionI am not aware of another feat that compares to the accomplishments needed to build the dome over Santa Maria del Fiore, and please note that I include only projects in recordedhistory.  We can only speculate how the pyramids in Egypt and Stonehenge in England, among others, were constructed.  It is difficult to cite acts of genius when so little is known about the process of building these and other amazing ancient structures.

Though some of the means and methods used in constructing the Dome are hidden within the structure, we have enough documentation to form an understanding of how it was designed and built (as an example, we can confidently assert that extra-terrestrial assistance was not involved).  The Wool Guild kept detailed accounting records of their payments for material and labor over the 150 years of Cathedral’s design and construction, and they still exist.  There are also specifications and many sources of observations and testimonials regarding the work.

Possible rivals to the Santa Maria del Fiore dome that come to mind are the Eiffel Tower in Paris, the Panama Canal, the Brooklyn Bridge in New York, and I am sure there are other endeavors not known to me.  These projects are remarkable in the amount of genius and courage required for their completion, and an argument could be made that they equal that which went into the building of this dome.  All were revolutionary at the time they were built, and have successfully withstood the tests of time.  They involved men with incredible vision and genius.  However, in my opinion these projects fall short because none began with as much uncertainty and risk, and they did not require such a broad scope of innovations in so many different areas.

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The original planners of the Santa Maria del Fiore cathedral blithely threw the ultimate success of their city’s most prominent structure to providence, and 120 years later their successors were still waiting for this providence to appear.  The financial and emotional commitments several generations of Florentines made in building a cathedral they had no idea how to complete is amazing, and in my opinion unique in history.  Ultimately their providence was delivered by a tiny man who even his friends considered irascible and difficult.  But he possessed one of mankind’s most fertile minds, and single-handedly solved the many complex problems required to construct this massive dome.  I know of no preceding or subsequent human endeavor that blended more courage and genius than this one.

EPILOGUE

If you were to tell someone that America was discovered from atop the dome at Santa Maria del Fiore, the person would probably become uncomfortable and look for the nearest door.  But to some extent the dome actually contributed to the discovery of the New World.  Amerigo Vespucci was born in Florence in 1454 where he studied science and astronomy before following Christopher Columbus in a quest to find a western passage to Asia.  While in Florence it is reported he used the dome as an observatory to advance is astronomical understanding.  These studies eventually led to his development of a new system to compute the Earth’s longitude, allowing him to calculate the circumference of our planet to within 50 miles.  This enabled Amerigo to be the first to realize that the lands being explored were not the east boundaries of India, but an unknown land that today bears his name: America.  His work atop the dome at Santa Maria del Fiore certainly contributed to his ability to discover these new continents.

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<![CDATA[The Hoisting Problem]]>Wed, 22 Jun 2011 10:18:02 GMThttp://florencedome.com/blog/the-hoisting-problemThe height of the dome’s construction and the lack of ground-supported structure to support its centering combined to create some tremendous problems.  Hitherto most hoists were powered by cylindrical tread-wheels where unfortunate men acted like hamsters, walking in place in a round cage all day to rotate a horizontal shaft, using their weight to lift loads by means of a pulley above.  Such mechanisms dated back centuries, but they were slow and limited in the size of loads they could lift. 

There were other lifts that could lift heavier loads by having horses or oxen walk in a circle, rotating a vertical shaft that was geared to turn the horizontal shaft connected to a pulley above.  However, this method had a fundamental drawback: while it could lift heavier loads it could not effectively lower them down into position.  Animals do not like to walk backwards, so to lower the loads once they reached their desired height it was necessary to remove the oxen’s yokes, turn them around, re-yoke them and walk them in the opposite direction.  This time-consuming process significantly slowed the construction.

Some of the stones needed to build this dome weighed several tons each and needed to be precisely fit into position hundreds of feet above the ground.  The human treadmill option simply could not do this work so the need to use of beasts of burden was obvious.  The issue of how could these loads be raised to such vast heights and then gently lowered into place became prominent.  The solution Filippo developed to solve this problem solidifies his place in history as one of mankind’s greatest inventors in my humble opinion. 

Filippo must have relied on his past apprenticeship as a clock maker to invent a hoisting machine with intricate gearing and a clutch mechanism that enabled it to lift and lower great loads while the oxen continued to walk in the same direction.  While the oxen rotated a vertical shaft to which they were tied, a series of cogged wheels were used that could be engaged or disengaged by a workman on the ground via the clutch mechanism.  By altering which cogged wheel was employed the direction with which the hoist operated could be reversed easily.

The hoist Filippo invented was a grand and celebrated machine, about the size of a small house, sitting on the floor of the cathedral directly below the opening.  It proved to be one of the most critical developments in the dome’s construction, and the reversing clutch would become one of the fundamental parts of modern engines.  Giorgio Vasari, one of Filippo’s biographers wrote a century later that this machine was so ingenious that “one ox could raise what six pairs could scarcely have raised before”.

Most sources I have researched agree that Filippo’s hoisting device was decades, if not a century ahead of its time.  The hoist was fast compared to previous machines, raising about fifty loads per day.  It is estimated that 60 to 70 million tons of material went into the construction of this dome, and all were lifted with this amazing device.

Filippo also invented load positioning machines used on the scaffolding above to move the loads laterally to their needed place in the construction.  True to form, Filippo did not document his inventions but other people did, including Leonardo Di Vinci several decades later.  It is believed that some of Leonardo’s famous sketches are renderings he made trying to document mechanisms invented by Filippo Brunellschi.*  In regard to the dome, one of Leonardo’s earliest assignments as a young apprentice was to help build the bronze sphere atop the lantern, crowning the dome. 

* As an interesting side note, Filippo and Leonardo had remarkable similarities: both were acclaimed artists and inventors, both used secretive coded language to record their ideas, and both experienced dramatic failures when they dabbled in hydrology (the science of water movement).  Filippo’s failure occurred when he concocted a plan to dam a river to flood and destroy Florence’s enemy, the nearby city-state of Lucca.  It ended disastrously when Lucca hastily built a dike to protect their city from the man-made flood, then snuck across the river and breached the dam onto Florence’s encamped army.  It humiliated the Florentines and greatly tarnished Filippo’s reputation.

Leonardo’s adventure in hydrology occurred sixty years later when he devised a scheme to re-route the Arno River, supposedly to improve Florence’s access to the sea, but the proposed plan would also conveniently divert the river from flowing through another enemy city-state downstream…Pisa.  Without the Arno River, Pisa would probably cease to exist.  It is likely that Leonardo worked closely with another illustrious Florentine, Niccolo Machiavelli, on this project.  The work to divert the river was underway and going well when a freak storm destroyed much of their progress.  Due to the mounting costs, the city leaders decided not to revive the project.

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<![CDATA[The Centering Problems]]>Wed, 15 Jun 2011 10:46:40 GMThttp://florencedome.com/blog/the-centering-problemsThe process of building a masonry dome without centering was revolutionary and, as alluded to earlier, raised considerable skepticism.  In smaller, more conventional domes and arches the centering gives the masons a form to place their material upon.  This wooden form holds the masonry and wet mortar in place while it hardens, at which point it is removed from beneath.  But these forms also provide a valuable measuring instrument to the masons.  The forms can be built by carpenters on the ground to exact dimensions and then be hoisted into place above.  Filippo’s plan abandoned these conveniences (not by his choice) and thereby created several major headaches.  The problem with measurements will be the first one discussed, and its actual solution remains somewhat mysterious.

The dome was not spherical but was to be built to what is called a “pointed fifth”, a gothic feature popular in the cathedrals in northern Europe.  All this means is that the center of the dome was not the radius point the dome would follow as it ascended (like the half orange peel or the Pantheon); each of the eight faces of the Florentine dome would have a different radius point.  The pointed fifth refers to the position of this radius point…it would be a distance one-fifth the diameter of the opening from the opposite side of the dome.  Since without centering all dimensioning must be done far above ground, the question becomes: how do you establish eight radius points, each being 170 feet in the air and about 28 feet inside the dome’s platform?  We know that each of the eight segments (or faces) of the dome had its own master-mason and crew, and each had to be built exactly like the other seven.  We also know that as the dome ascended and closed in toward the oculus the angle of the masonry angled in toward these radius points, becoming 60 degrees to horizontal at the top.  This meant that precise measurements were needed both for the inward curvature of each segment and the angle at which the masonry was sloped.
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The curvature issue may have been solved by using eight identical wood templates placed at each corner of the dome.  These templates would have been lifted incrementally as the masonry rose and had their respective angles carefully coordinated with plumb lines.  The angle at which the masonry was placed does not present as easy a solution.  It could be that carpenters were able to cantilever eight structures 30 feet out into the abyss and attach long wires stretching to the opposite dome segments.  We know that cantilevered wood structures were necessary for the masons to do their work, but a 30 foot cantilever would be difficult since the largest trees available were little more than thirty feet long.  Splicing the logs could have worked, but I think a more likely solution was that the masonry’s angle to level was calculated by Filippo who then used a tool or mechanism to convey the exact angle to the masons at each segment. 

Each week the masons added about one layer of bricks onto the dome, meaning it ascended at a rate of one foot per month (grass grows at about this rate).  The next problem presented by not centering the dome’s construction was how to hold the masonry in place while the mortar hardened.  At the bottom of the dome this was easy…the joints between the layers of brick were flat, meaning gravity would hold them in place while the mortar hardened.  However, as the dome rose and the joints started sloping at increasingly steeper angles inward, the bricks laid in wet mortar would not stay put…they wanted to slide down, bounce off the scaffolding, and land on the floor over 200 feet below. 

To understand the mason’s challenge, imagine eating a plate of food from a table sloping like the roof of a typical house.  It would be an awkward meal since gravity would be constantly trying to push the plate into your lap.  A possible solution would be to wedge the plate between two objects projecting from the sloping table that would prevent your plate and its contents from sliding downward.  This was the concept behind the herringbone brick pattern Filippo devised. 

The sloping brickwork was laid using principals of that old architectural stalwart: the arch, only in this case it did not span an opening, it enclosed one.  Like the walls that resisted hoop stress forces in an arch or a dome, the projecting bricks were placed in a way that allowed the bricks in between to transfer their downward load sideways.  Since these rows of bricks were 5-6 feet thick there was a lot of weight pushing downward.  The sketch below is representational of the concept it is believed Filippo used.  The exact configuration of the herringbone brick patterns is unknown.
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The last problem with his radical plan was basic human fear.  Conventional centering placed the workmen outside the dome as it ascended, and the wood centering blocked their view of the distance below them.  Filippo’s plan placed them inside the dome and thus they looked straight down to the cathedral floor, and certain death, from their scaffolding.  This became more harrowing as the dome neared completion and their work was at ever-greater angles downward.  To calm the workmen’s nerves, and increase their productivity, Filippo designed structures beneath them to hide this gaping abyss and to catch them if they did fall.  It is truly remarkable that there were only three deaths recorded during the fifteen years of the dome’s construction.

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<![CDATA[The Genius - Structural System]]>Mon, 06 Jun 2011 16:41:18 GMThttp://florencedome.com/blog/the-genius-structural-systemTHE GENIUS

While the courage to build the dome belonged to many generations of Florentine leaders and visionaries, the genius that made it happen was mostly attributable to one man: Filippo Brunelleschi.  In my opinion it is miraculous that a man with no structural training could create a structural design that was so intricate and correct.  To do this Filippo relied only on his studies of ancient ruins, his creativity, and his intuition.  For this structure to stand many of its structural elements had to be stronger than anything built before in history.  It is in some ways mystifying how he was able to conceive of some of his methods to meet the dome’s structural challenges.

As stated earlier there were three primary challenges presented by the construction of this dome: the structural system, the centering issue, and the lifting of materials so high above the ground.  Each of these presented problems never before encountered at this scale, and construction could not begin until all three problems were solved.

It is important to realize that many of the construction items we take for granted today were not available.  Steel and concrete would have simplified the structural design and centering issues; motorized lifts and power tools would have obviously made the construction work much easier.  The sophisticated measuring devices we depend on today at construction sites would have been a godsend to these workers.  It is sometimes hard for us to imagine the world as it was in 1420.  Below I will discuss the three primary challenges and how Filippo dealt with them using the means at hand.

The Structural System  

Domes were relatively common in 1420, but one of this size and configuration was unprecedented.  Decisions made fifty-four years before mandated that the dome be built on a fourteen foot wide octagonal platform about 170 feet above the cathedral floor.  This platform sat atop a thirty foot high drum, or tambour, where the large circular windows we see were placed.  It had been decided in 1367 that there be an inner and outer dome, and Filippo determined that the inner dome be seven feet thick of solid masonry at its base, tapering to five feet thick at the top.  The outer dome was to be almost three feet thick at the base and taper to about one and one-half feet thick at the oculus. 

The 1367 decision also required that the dome would have no flying buttresses to counter the hoop stress forces; these forces were to be contained by using a series of horizontal tension rings (acting like the glue around the second orange peel).  But of course this long-ago decision gave no details as to what these tension rings would consist of or how they would be made part of the structure.  These rings would be one of the first hurdles to overcome.

If you were assigned the task of designing a long chain for pulling an extremely heavy load, stone would probably not be the first material you would consider.  Stone reacts very well in compression, or when it is being squeezed, but it is weak when being pulled apart in tension like a chain.  The rings around the dome (sometimes called chains) would have to resist enormous tension forces resulting from the aforementioned hoop stress.  If steel had been available in 1420 the tension ring problem would have been easy to solve because steel has excellent tensile properties, but of the materials available only iron and wood had reasonable resistance to tension.  Iron was rust-prone and difficult to forge in the sizes and lengths needed, while wood had a tendency to splinter, warp and decay. 
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The tension ring issue had to be solved or the dome would certainly collapse, and one of the first innovations Filippo developed was a method to effectively use stone for these tension rings.  Actually Filippo devised two types of rings, one of stone and one of wood, but the stone ring design was intriguing.  It consisted of two rows of 17 inch wide blocks of sandstone laid horizontally several feet apart from each other.  The blocks were nearly 8 feet long and had notches chiseled in them where smaller stone blocks were inserted cross-wise connecting the two rows, similar to the cross-ties in a railroad track.  The 8 foot long blocks were connected to each other length-wise with iron fittings.  There were four of these rings constructed at increments as the dome rose.  You can see evidence of the first ring at the base of the dome just above the round windows.  Here you see a row of stones sticking out…these are the transverse stone blocks (railroad ties) that connect the two rows of the first stone ring. 

Despite extensive studies using modern scanning technologies, some aspects of these chains remain unknown.  The specifications Filippo developed stated that iron rods and chains would be incorporated into the stone chains.  Magnetic scans failed to reveal the presence of iron and it is possible we will never know how (or if) the iron was used.
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The wood chain was made from 20 foot long chestnut logs about 12 inches square that were anchored to each other with oak plates and iron rods.  There were to be four of these chains in the dome, but for some unknown reason only one was built.  However this ring had one very interesting consequence beyond the structure.  It was during the installation of the wood ring that Filippo exposed the folly of his rival Lorenzo being his equal in status and pay for the dome’s construction.  Like every aspect of the design Filippo’s plans were intricate and unrecorded, existing only in his head.  When the wood ring was about to be installed Filippo suddenly became seriously ill and confined himself to bed, though some suspect his sickness was feigned.  In his absence Lorenzo was forced to take charge of the work, and specifically to install the wood chain.  It went miserably and soon everyone, including Lorenzo, was forced to admit that only Filippo knew how to build this dome.  His arch-rival was demoted and became mostly irrelevant throughout the remainder of the work. 

These unorthodox and ingenious tension rings have obviously served their purpose over the last 600 years, but they do so in conjunction with other structural innovations Filippo developed.  To help explain another serious structural problem I will again resort to fruit, this time a banana.  The hoop stress demonstration using an orange was not exactly applicable to Florence’s dome because its base was not round like the orange; it was octagonal with eight 45 degree vertical corners or ridges.  A banana has similar ridges and when you peel a banana you will notice that it always separates at these corners.  Filippo understood that these eight vertical corners were the most vulnerable part of the dome and he designed an ingenious vertical and horizontal skeleton system that strengthened these corners while integrating them with the tension rings.  Once more he found answers to problems that no one had previously confronted, and did so successfully.
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<![CDATA[The Courage]]>Tue, 31 May 2011 09:10:47 GMThttp://florencedome.com/blog/the-courageTHE COURAGE

Courage is a subjective term.  Acts that some might consider courageous might be thought of as foolish by others.  Often the only difference between a courageous endeavor and a foolish one rests in its outcome.  The definition I choose for this essay is thus: the act of taking risks to achieve a desired outcome.  With this definition it is possible to measure courage by determining the level and extent of the risks one is willing to accept.  Of course the ultimate act of courage involves risking the most valued possession any person has: their life.  Next to this sacrifice most risks pale in comparison, but most would agree that risking your reputation and livelihood for a desired goal is significant.

All construction projects require some courage, and that needed to construct the dome at Santa Maria del Fiore was not exceptional for the masons and workmen who climbed up to do the work.  A few fell to their deaths, but sadly this was not uncommon in construction projects at the time, nor is it today.  The world in 1420 however was a much more callous place for workmen than it is now.  When a workman perished his widow and family would be given the wages he had earned to the moment he fell, his funeral would be paid for, and nothing more.  His family would sometimes be left to beg or starve.  Fortunately the number of deaths reported during the construction of the dome was remarkably low considering its enormous scope.

The courage I speak of in this essay involves the process leading to its actual construction, not the work itself.  The fact that Florence poured so much of its recourses over 130 years into the massive walls and vaulting of the cathedral without having the vaguest idea how to enclose that enormous hole in the roof is extraordinary; a bold statement of optimism and confidence that easily could have ended tragically.  If one can imagine the skyline of Florence without their dome… if it had never been attempted or if it had collapsed during construction the city and its history would be drastically different than it is today.  They risked so much pride, time and treasure in their goal to build something unprecedented in its size, and ended up achieving something beautiful as well.  Additionally they did this at a time when horrible plagues and military conflicts were constantly at their doorstep. 

The dome has withstood earthquakes and a steady flow of lightning strikes over the last 600 years.  It remains a solid and powerful symbol above the city of Florence and is, in my opinion, one of the world’s proudest monuments to courage.  

 

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<![CDATA[Where Do We Go From Here?]]>Sun, 29 May 2011 14:17:34 GMThttp://florencedome.com/blog/where-do-we-go-from-hereWHERE DO WE GO FROM HERE?

So there it was…in 1418 Florence had a massive church with massive walls and columns, and an enormous hole above that no one had a clue how to cover.  The divine providence the planners had hoped for had yet to provide an answer, so that year the city decided to hold a competition.  A considerable sum of money was offered to anyone who could solve the riddles this construction posed.  There were three major problems: how to structurally design a dome this huge using masonry (since no other building materials were available), how to support the dome while the mortar holding the masonry together hardened, and how to transport the building materials so high above the ground.  All three of these problems required unique and untested solutions. 

Eleven proposals were offered by architects from throughout Tuscany, but one in particular intrigued the Wool Guild and its appointed council.  It was submitted by a goldsmith and clock-maker named Filippo Brunelleschi.  Filippo was a character well-known to the members of the Council and to most of Florence.  He had grown up close to the cathedral construction site and his father served on the council that decided to increase the size of the dome in 1367.  His prime notoriety came from being a finalist in the design of the baptistery doors fifteen years before.  The design and production of these bronze doors were the focus of an intense competition in which artists were told to provide a panel showing the biblical story of Cain and Abel.  Two of the panels submitted stood out…those of Filippo Brunelleschi and Lorenzo Ghilberti.  Ultimately Lorenzo’s design was selected, though to this day art scholars debate who should have won this lucrative commission; both works were so excellent.  Nevertheless, Filippo left Florence in a fit of anger upon learning of his defeat and headed to Rome.  To some extent this spiteful journey became a significant historical event.

Rome at this time was a shell of its former self.  A city that once had a population of one million now had about twenty-thousand residents.  The Catholic Church was divided and had two popes, one in Rome and the other in Avignon, France.  Much of the remaining populace consisted of vagrants and hucksters preying on visitors who came to Rome to see Christian relics.  The beauty that had been developed and refined during the Roman Empire was scorned by the Church and the people living there. These ancient structures had become an architectural scrap yards where people went to scavenge marble columns, bricks, and tile to use in their new churches and buildings.  Luckily the Pantheon was spared this fate having been consecrated as a Christian church centuries before.  

Filippo was one of the first persons to appreciate the architectural beauty and technical accomplishments made by the Romans, and his journey started a pilgrimage that some consider the beginning of what we now call the Renaissance.  What he and others did was study Roman antiquity despite the fact that it was in conflict with Christianity, and afterwards they incorporated their knowledge of these pagan structures into new projects.  Filippo spent many years in Rome measuring and studying what remained of that Empire’s architecture.  In the back of his mind he knew that the dome over Santa Maria del Fiore would soon need to be built, so he spent much of his time in Rome studying the hulking ancient structures looking for structural clues as to how they were built.  He was armed with this information when he returned to Florence and went before the Council in 1418 with his plans to build the dome.

But as noted previously the structural knowledge needed to construct this dome was just one of the vexing issues confronting the competition entrants.  Foremost on many minds at the time was how to “center” the dome.  Centering is the term alluded to earlier involving temporary supports to hold the dome’s masonry in place while the mortar between the bricks dried and hardened…a lengthy process.  It had been deemed impossible to build a wooden structure high enough to support the dome’s construction. No one had an answer and some doubted the dome could ever be built; that this hole above their cathedral’s roof would become a permanent and shameful stain on Florence.  Supposedly one of the competition entrants suggested that gold coins be sprinkled on the floor and then the church be filled it with dirt high enough to allow the dome to be built.  Upon completion the city would then send in an army of peasants to remove the dirt in search of the gold coins.  There is no evidence that this proposal was taken seriously.

To solve the centering problem Filippo proposed a daring plan…that there be no centering.  Filippo was already viewed by many in Florence as eccentric, but this proposal led them to also consider him a lunatic, and he fueled their beliefs by steadfastly refusing to divulge how he proposed to actually do this.  The fact that he was not forthcoming with his plans was probably not surprising to those who knew Filippo.  He had always been extremely secretive about his ideas, developing codes for his writings (a concept adopted by Leonardo Di Vinci some fifty years later).  His concern about rivals stealing his concepts was the reason he refused to reveal how he proposed to center the dome’s construction, but his reticence was not appreciated by the council and led to angry exchanges and stormy meetings.  Nor did it help Filippo’s cause that he had never before served as an architect, though this was not as unusual as one might expect.  Architecture was not a profession people were trained to provide at this time, these services were routinely assumed by painters, sculptors, master masons, and goldsmiths.  Nevertheless for a while Filippo could barely go out of his house without being barraged with sarcasm and insults from people on the street.  But throughout this turmoil the Council could not ignore him, because they really had nowhere else to turn.  

Over the next two years the Council dithered.  It is not known whether Filippo acquiesced and provided details of his plans for the dome’s construction, but certainly a transformation took place.  Filippo suddenly started receiving other architectural commissions throughout the city, some that included small domes.  Then in 1420 the Council cautiously paid him to provide specifications for the construction of the dome at Santa Maria del Fiore.  It appeared that Filippo had won the competition and would be the architect for this incredibly challenging project, but in the midst of his redemption the Council threw two ironic twists at him.  First, he would not be rewarded the monetary prize for winning the competition even though his concepts were chosen, but this was minor compared to the other twist.  They decided that Filippo would be the co-architect for the project and his partner would be his hated arch-rival, Lorenzo Ghilberti, the man who uprooted his life twenty years earlier in the Baptistery Doors competition. 

So there they stood on that August morning in 1420, high in the air on an octagonal platform, wondering how this dome could safely rise to heights never before attempted.

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<![CDATA[About Domes]]>Sun, 29 May 2011 14:07:07 GMThttp://florencedome.com/blog/about-domesABOUT DOMES

To understand domes it helps to first understand the principles behind the arch.  While most people would agree that the wheel has been the greatest invention in our history, the arch is not far behind.  It revolutionized architecture and our capacity to control our environments.

Our earliest buildings consisted of mud and timber, but eventually stone became widely used.  Stone was durable and fire-resistant: a popular trait since inside fires were needed to heat and cook.  However, as good as stone was for building walls, it was equally bad for building roof structures…its weight and size restraints limited the area you could enclose.  If you could find a stone massive enough to span the distance between two walls or columns you then had to figure out how to lift it into place.

The arch solved this problem by allowing smaller, easy-to-lift, pieces of stone to be used to span the distance between two walls.  The stones were bound together using friction which diverted the gravitational forces piece-by-piece to the outer walls.  But to make an arch work there were two important things that needed to happen: the stones needed to be cut so that the joints aligned with the arch center, and a temporary form was needed to hold the stones in place until the top piece, or keystone, was placed.  The development of the arch allowed buildings to soar in comparison to their predecessors.
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The use of domes in architecture dates back over two thousand years.  Basically a dome consists of numerous two-dimensional arches rotated around their midpoint creating a three-dimensional structure.  However, when these arches are rotated something remarkable happens: the keystone, that crucial element at the top of the arch, becomes unnecessary when they transform into a dome.  The very top of the dome can be left open without compromising its structural integrity.  This hole is also known as an oculus, and it allows light to enter the space.
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The primary challenge to building a dome is the outward pressure placed on the structure surrounding it.  This pressure is calledhoop stress and it can be easily understood by performing a simple experiment.  Take an orange, slice it in half, and remove the inside fruit.  Place the two peels on a board so that they resemble small domes.  Around one peel trace the outline of its circumference on the board with a pencil.  Then take the second peel and apply a continuous bead of glue adhering its entire base to the board.  After the glue hardens take your hand and press down on the first peel (in a way that simulates how gravity puts force on a dome).  You will see that the flattened peel has pushed out beyond the outline you drew around its base.  When you place the same pressure on the second peel you will see there is much more resistance to the pressure you apply.  The glue has countered the hoop stress forces on your small dome.  

The Pantheon in Rome is perhaps the purest example of a dome to be found.  It was built out of concrete by the Roman emperor Hadrian some 1200 years before work began on the Santa Maria del Fiore.  Inside this dome one can see progressively smaller recesses, or coffers, as the dome extends upward toward the oculus.  These coffers not only reduced the weight of the massive structure, but divided the dome into a series of structural ribs and rings.  The hoop stress forces previously mentioned were dealt with by the use of 23 foot thick solid brick and concrete walls around the perimeter of the dome, but even walls that thick could not adequately resist the hoop stress forces and cracks appeared.

The Pantheon’s dome spanned 142 feet across, about the width intended for Florence’s dome, but there were major differences and complications…the first one being that the art of using concrete had been completely lost in the Medieval Ages.  The Romans had developed this product that could be poured in fluid form onto temporary wooden forms and allowed to harden.  After reaching its desired hardness the wooden forms were removed exposing the finished underside of the dome.  Numerous examples of this construction technology could be seen in the ruins of Rome at the time Florence was planning their dome, and it must have frustrated architects that the technology was no longer available. 

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Another reason the architects for Santa Maria del Fiore could not use the Pantheon’s dome as a prototype was its height.  The base of the dome at the Pantheon was about 70 feet above the floor.  This height enabled the Roman builders to erect wood scaffolding to support the forms the concrete was poured into, and to hold this concrete in place while it dried and hardened.  Wood scaffolding had always been an essential element for building masonry arches and domes because it could hold the stones or bricks in place while the mortar binding them together dried and hardened, a process that could take a year or more.  Because wood warps and shrinks as it ages it was very challenging to build these temporary structures. There were limitations as to how high you could reliably build wood scaffolding, and the base of the proposed dome in Florence was to start at about 170 feet above the floor and top off at about 300 feet, more than twice as high as the Pantheon.  Knowledgeable people understood that wood scaffolding could not be built that high.  Again the leaders planning the cathedral in Florence casually disregarded this fact, and continued building the walls of the church while having no idea how this problem could be overcome.  

There were still more differences: the base of the Pantheon dome was circular while the Florentine dome was to have an octagonal configuration, and the dome itself at the Pantheon was spherical, while the dome in Florence was to have a “pointed fifth” or cone-like shape. 

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<![CDATA[Introduction and Background to the Dome]]>Thu, 26 May 2011 23:33:09 GMThttp://florencedome.com/blog/introduction-and-background-to-the-domeINTRODUCTION

On an August morning 590 years ago a group of workmen climbed about 250 steps and walked out onto a fourteen foot wide platform.  Above them was sky, and looking 170 feet straight down they saw the floor of a cathedral.  Across they saw a large octagonal hole in the cathedral’s roof measuring about 140 feet across (almost the width of a football field).  On that day they would begin construction of a dome over this opening.  “Are you sure this will work?” was surely on many of the workmen’s minds that morning, and on the minds of thousands of people on the streets far below…nothing like this had ever been done.

History records a tremendous number of feats undertaken by societies and individuals that moved mankind beyond previously held boundaries.  Many of these feats have involved remarkable courage, especially heroic efforts by men and women to unshackle themselves from the vices of tyranny.  Other feats have involved individual genius where established norms and practices are uprooted by daring artistic and technological achievements and inventions.

The purpose of this article is to make the case that no single feat in recorded history has involved a greater combination of courage and genius than the construction of this dome over Santa Maria Del Fiore in Florence, Italy.  I acknowledge that the courage required for this construction does not compare to the courage demonstrated by men and women who have fought and died in wars, revolutions, and in defense of their convictions and faith.  Nor do I contend that the genius needed to build this dome compares to inventions that have permanently transformed our civilization.  I simply believe that no feat more effectively combined both courage and genius than the effort that went into the construction of this dome.

BACKGROUND

It is almost humorous how the Florentines found themselves in the situation where the dome needed to be built in the first place.  It is a story whose roots went back almost 130 years before this August morning in 1420.  As a proud and prosperous republic in the 13th century, the leaders of Florence determined that they should construct the most magnificent cathedral known to man.  This was quite a mission.  In the previous 200 years some stunningly large and beautiful cathedrals had been completed in Northern Europe.  

This was a time when Florence was the financial capital of the world, the Wall Street of its time.  Its currency, the florin, was the international monetary standard and their banks were dominant throughout Europe and parts of Asia.  Internally the city was home to many prosperous commercial enterprises, each controlled by associations of their respective tradesmen and master craftsmen called guilds.  The role of these guilds was to oversee the quality and practices of their industry, but they were each also given specific civic, religious, and charitable responsibilities.  The responsibility for overseeing the design and construction of Florence’s preeminent cathedral was given to the Wool Merchants Guild, the city’s wealthiest and most powerful.  Florence’s wool industry imported English wool and processed it with exotic dyes from Tuscany and Asia, making the most sought-after cloth in Europe.  The Wool Merchants Guild assigned a Council to administer the cathedral project who then appointed knowledgeable architects and craftsmen to perform the work. 

In the previous centuries architects had advanced their structural mastery to allow cathedrals to soar in height.  The Cathedral of Notre Dame in Paris was built 102 feet tall and was soon eclipsed by a cathedral in Chartres that reached 120 feet.  As more Cathedrals were built throughout Europe architects continued to test the structural limits until, as you might expect, a Cathedral in Beauvais, France collapsed.  It had attempted to reach 157 feet, and though some of this church remains today it appears as an unfinished monument to reckless architectural ambition.  

Another ambitious church was the Hagia Sophia in Istanbul, Turkey.  This amazing structure was begun in 532 A.D. and included a beautiful dome, 102 feet in diameter, with forty windows around its base.  The light from these windows gave visitors the impression that the dome was suspended from heaven, an impression proven wrong when it collapsed soon after being built.  The dome was rebuilt and then collapsed again in the 10th Century.  It was modified and rebuilt once more and today continues to thrill visitors, but it also serves as an example of overly bold architectural ventures.  

Despite the time and distance between these structural failures and 14th Century Florence, the Wool Guild planners were well aware of these failures.  However, the traits of prudence and pragmatism were not highly regarded in Florence at this time, and in the year 1296 A.D. construction of their grandiose cathedral moved forward.

THE WORK BEGINS

The Wool Guild Council chose a site in the center of the city and began building foundations for the new cathedral.  The plans featured a long nave, aisles, and three transepts intersecting to create a large crossing, over which a dome would be placed.  A large model of the finished cathedral was placed next to the construction site for the citizens to marvel at and the workmen to use as a guide.  At this time the architects had no idea how this dome would actually be constructed; they were led by a faith that God would provide an answer when the time to build it came.  Over the next seven decades the walls of the nave were built and vaulted.  Work was about to begin on the part of the structure that would support the dome.  The aforementioned model intended to guide the design of this area had already collapsed from its own weight.  Undeterred by this inauspicious fact, the Council decided to modify their plans.  They determined that this part of the cathedral should be even larger, and the height and span of the dome should be even greater.

In 1367 another model of the cathedral was commissioned and placed inside the finished portion of the cathedral.  The architect for the modified design was named Neri di Fioravanti, and he not only showed the dome to be much larger, but to include no flying buttresses.  These buttresses were a necessary feature of the cathedrals already built in northern Europe.  They transferred the lateral forces from these tall structures outward, and down to the ground.  But as previously mentioned, even flying buttresses were not enough to prevent the collapse of the cathedral in Beauvais, France in 1284.  The new parameters for the dome Neri designed required vaulting that far-exceeded what had been attempted at the collapsed churches in Istanbul and Beauvais, and it would begin much higher above the ground.

Nothing exemplifies the incredible spirit and faith of the Florentines at this time than this fact: between 1348 and 1400, during which much of the planning and construction of the cathedral took place, there were six separate outbreaks of the Black Plague.  In1348 the plague claimed over half of Florence’s population, and subsequent outbreaks continued the devastation.  The 1400 manifestation took 20% of the remaining population of the city.  If this wasn’t enough to squelch the ambitious plans of the city, they were also frequently besieged by invading armies during this period.  The fact that the city moved on so boldly during these crises speaks to the amazing confidence and motivation they had.

Over the next several decades the model of the new dome design became a revered item among the builders and the citizens of Florence.  The model was large; thirty feet long, fifteen feet high and made from bricks and mortar.  Annually the persons responsible for planning and building the cathedral were brought to the model, forced to place their right hand on a bible, and to swear to follow its intent.  Sadly this model was demolished a century or so after the cathedral’s completion.  Presumably it did not collapse from its own weight as its predecessor had.  

The dome Neri presented in 1367 did not bother to include structural design information showing how the dome could be built, but it did call out for the use of an inner and outer dome.  This was a practice that had been used in middle-eastern architecture where the inside dome served primarily to support the loads and the outside dome served to protect it from the elements.  He also envisioned the use of chains encircling the dome to take the place of the flying buttresses, but said nothing about what these chains would be made from or how they could be built.

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