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Brunelleschi's Dome -- a Monument to Optimism


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 renaissance Florence, Italy--the Dome of Santa Maria del Fiore. The year was 1418.

Such an undertaking 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 have to span an opening of 138 feet, begun at a height of 177 feet, 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 great weight of the dome could have no internal or 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 full weight of the dome.

There was one final problem--no 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.

Was there an architect in all of Italy with the creativity and the engineering skills--the unshakeable optimism--to build such a dome? There was. His name was Filippo Brunelleschi (pronounced Broon-ell-es-kee).

Brunelleschi was a native of Florence. Like most sculptors and architects of Renaissance Italy, he had began as a silversmith, then graduated to sculpting marble, and learning to build with stone. He had a head for math and spent the previous 20 years in Rome studying and measuring all the great buildings of antiquity. Above all, he marveled at the great dome of the Pantheon. The Roman engineers had had the advantage of scaffolding and pouring quick-setting concrete from which the dome was built. Alas, the knowledge of 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 build his dome with 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 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.

It was easy--when you knew how.

Brunelleschi was awarded the commission. His plan called for building two domes--one within the other. The inner dome would be built first, and like the frame of an automobile, contained all the necessary supports that would hold everything together. The inner dome would contain several horizontal supports, consisting of a series of sandstone and wood beams and iron chains that would circle the dome like the hoops of a barrel, to keep the structure from spreading outward and collapsing the cathedral walls. Because the dome would be an octagon, the vertical supports at each of the eight corners, would curve inward toward the center, with two additional vertical supports between each corner support, 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 domes and arches. 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 this luxury. To get around it, he had the building bricks laid 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 this, row upon row, upward and inward, the circle ever closing with each new row.

Beside this, there were a multitude of other problems to be overcome. For one, as the dome rose upward and ever inward, workmen became increasingly afraid. With no visible means of support (and not understanding the law of compression), they believed the entire structure would collapse from 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. Not a problem, as Brunelleschi would purchase bricks from outside suppliers, but first he had to design and build special ships to have the bricks transported to Florence.

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 widely copied by others including Leonardo de Vinci. The hoist not only raised material, it had a swinging arm for moving 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 putting in 14-hour days and needing to eat two- and three-times a day, 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 to eat. To save life, he designed a special leather harness, each with tie line attached, to prevent workers for falling to their death.

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 heat-treated tiles designed specially for easy assembly and maintenance.

Between the inner and outer domes, is a cavity for stairs leading up to an observation platform at the summit of the dome. There are 463 steps that feel like 1000 when you reach the top. Making the climb and taking in the view is a must-do for today's 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, one of the greatest achievements of Renaissance architecture.

The dome has survived hurricane winds, and several 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.


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