A Monument to Optimism - The Dome of Florence
History - World Released - Sep 30, 2013
It was some contest, and it was some prize. The contest was finding a way to stand an egg on its end. The prize was designing what would become the signature architectural landmark of Florence, Italy--the octagonal Dome of Santa Maria del Fiore. The year was 1418.
Creating the Dome would require more than mere artistic vision. It would require engineering techniques yet to be developed and something more: unshakeable optimism, for nothing like it had been done before. Indeed, few believed it could be done. The Dome would span an opening of 138 feet, begin at a height of 177 feet above the ground, and rise to a height of 375 feet. To put it into perspective, the dome would rise from an opening 18 stories above the street, and top out at the equivalent of a 38-story building. Just getting building materials up to a height of an 18-story building to begin work would be a formidable undertaking in itself.
That was not all. The walls to support the weight of the Dome could have no external supports. Indeed, the opinion makers of Renaissance Italy had decreed that anything resembling Gothic Architecture--i.e. flying buttresses--would not be permitted. The walls alone, without lateral supports, must carry the great weight of the dome.
There was one final problem--no center scaffolding. The good people of Florence had taken an inventory and discovered there were not enough trees in all of Tuscany to produce the scaffolding necessary to reach such dizzying heights.
Those were the conditions: no flying buttresses, no internal supports, and no center scaffolding. Was there an architect in all of Italy with the creativity and the engineering skills--and the unshakeable optimism--to build such a dome? There was. His name was Filippo Brunelleschi. That’s Broon-ell-es-kee.
Brunelleschi was a native of Florence. Like most engineers and architects of Renaissance Italy, he began as a silversmith, then graduated to sculpting marble and building with stone. He had a head for math and spent 20 years in Rome studying and measuring all the great buildings of antiquity. Above all, he marveled at the great dome of Agrippa’s Pantheon. The Roman engineers had had the advantage of scaffolding and pouring quick-setting concrete from which the dome was made. The recipe for making quick-setting concrete had been lost during the Dark Ages, but this did not deter Brunelleschi. Instead of pouring a concrete shell, or building with stone, he would use brick and mortar which was lighter and just as durable. At the end of his time in Rome, Brunelleschi had worked out in his mind how he would build the octagonal Dome of Santa Maria del Fiore.
It was at a conference of architects and engineers that Brunelleschi presented his concept. He wouldn’t divulge all the details; he said his dome would be fully stressed on all sides like the shell of an egg and not require additional supports. He built a 1:12 scale model to demonstrate his method. None of the other architects had much to offer other than wanting the commission and having the necessary political connections to get it. To set himself apart, Brunelleschi challenged them to make an egg stand on end. After they all failed, he succeeded by pressing the blunt end down upon the table. When they answered that they could have done the same thing, he answered that they would make similar claims AFTER he had built his dome atop the cathedral.
Brunelleschi was awarded the commission. His plan called for two domes--one within the other. The inner dome was built first and like the frame of an automobile contained a series of horizontal and vertical supports that held everything together. The horizontal supports consisted of a series of sandstone and wood beams and iron chains that circled the dome like the hoops of a barrel, to keep the structure from spreading outward. Being an octagon, there were vertical supports at each of the eight corners, curving inward toward the center, with two additional vertical supports between each of the eight corners, for a total of 24 vertical supports. Coupled with the circular horizontal supports, the entire structure was a lattice work of cross members embedded within the brick-and-mortar walls. But how was it built without center scaffolding?
Center scaffolding is crucial in building arches and domes. Once center scaffolding is in place, rows of bricks are run up to the top of the scaffolding, and a keystone locks everything into place. Once the mortar sets, the scaffolding is taken down. Brunelleschi did not have that luxury. To get around it, he laid the building bricks in a herring-bone pattern that redirected the weight of the bricks against the vertical supports, instead of downward toward the ground. Once a row of bricks was locked into place, work proceeded on the next row, and continued like that, row upon row, upward and inward, the circle ever closing with each new row. To speed things along, he came up with his own formula for quick-setting cement that has since been lost.
There were a multitude of additional problems to be overcome. For one, workman became increasingly fearful as the dome rose ever higher and ever inward. With no visible means of support (and lacking faith in circumferential compression), they believed the entire structure would collapse under its own weight and they would fall to their death. So they went on strike. When they finally returned (for less pay), a plague struck the city and work halted yet again. In all, it would take 16 years to build the dome.
Another problem was the perpetual shortage of building materials. All the kilns in Florence could not produce bricks fast enough to meet the daily needs of building the dome. Brunelleschi purchased bricks from outside suppliers but had to design and build special ships to have the bricks transported to Florence. Theses ships were also used to transport marble that was used to build the cupola and adorn the church.
Yet another problem was getting bricks and large stones up 18 stories to the base of the dome. To lift 37,000 metric tons of material, including over four million bricks, Brunelleschi invented hoisting machines that were later copied by others including Leonardo de Vinci. The hoist not only raised material, it had a swinging arm to move material laterally. The most revolutionary aspect was a reversible gear. The reversible gear allowed loads to ascend and descend without the need of turning around the oxen team each time the direction was changed.
For the convenience of his workers, who were working from dawn to dusk six days a week, Brunelleschi built a cafe at the foot of dome, so they wouldn’t have to climb up and down 18 stories every time they wanted a hot meal. The architect was also safety conscious: he designed walkways with railings and leather safety harnesses for his workers. He even installed a safety net below the scaffolding, something unheard of at the time. In sixteen years there was but one fatality. How many construction sites in New York City or Chicago can make the same claim?
Once the inner dome was completed, work proceeded on the outer dome. The outer dome carried the roof. Brunelleschi created a unique external covering system that consisted of tiles designed specially for easy assembly and maintenance. The vertical ribs that are seen at each of the dome’s eight corners are for aesthetics and not load-bearing. Between the inner and outer domes is a cavity for two sets of stairs leading up to an observation platform at the summit of the dome. There are 463 steps that feel more like 1000 steps when you reach the top. Making the climb and taking in the view is a must-do for visitors.
Brunelleschi designed the cupola at the top of dome but did not live to see its completion. He did live to see the dome itself completed which is considered one of the greatest achievements of Renaissance architecture.
A century later, when Michelangelo planned the dome of St. Peter’s in Rome, and was told that he had an opportunity to surpass Brunelleschi’s, he said: “I will make a sister dome, larger, but not more beautiful.”
For nearly 600 years Brunelleschi’s dome has survived hurricane winds and a number of earthquakes. In a city brimming with breathtaking art and architecture, the Dome of Florence is the city’s most prized possession, and proof that one man with vision can do whatever he sets his mind on doing. However arresting to behold, the Dome of Florence is nothing less than a monument to optimism.
For more read “Brunelleschi’s Dome” by Ross King; for a virtual tour, including walking to the top of the dome, go to: www.youtube.com/watch?v=ohB1sNzpBe0
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