Episode 31: The Dome of Florence

Brunelleschi's Dome: How A Renaissance Genius Reinvented Architecture by Ross King is one of the many art and history titles on Audible, the leading source for audiobooks and other digital media.  You can download Brunelleschi's Dome as part of your free trial.  Go to audibletrial.com/itakehistory to sign up today.  You can support this podcast by getting a free trial.


I Take History With My Coffee Podcast
Episode 31
Title: The Dome of Florence  

“What man, however hard of heart or jealous, would not praise Pippo the architect when he sees here such an enormous construction towering above the heavens, vast enough to cover the entire Tuscan population with its shadow, and done without the aid of beams or elaborate wooden supports?”
Leon Battista Alberti,  On Painting, 1435

Welcome back to the I Take History With My Coffee podcast and thank you for continuing our exploration of the Early Modern period.

This episode is going to be longer than previous ones. There was no natural place to split it up into two separate episodes.  So, I hope you stick with me to the end and come away with a profound sense of appreciation for the achievement I’ll be discussing: the building of the dome atop the Cathedral of Santa Maria del Fiore in Florence.

Like art, architecture is meant to be seen.  So, once more, I have created a page with images related to Santa Maria del Fiore.  I have supplied a link in the show description.
  

During the medieval period, there was a sort of arms race that went on.  Cities vied with each other to build bigger and more splendid cathedrals.  A spectacular cathedral earned prestige for a city.  Beyond the religious context, it also meant prestige for the ruler who initiated and funded such projects.  Notre Dame in Paris.  St. Peter’s in Rome.  Westminister Abbey.  This cathedral one-up-manship became even more heated in the 13th century as the Italian city-states, flushed with commercial wealth, tried to outdo one another. In 1293, the city leaders in Florence decided it was time that the old church of Santa Reparata was replaced.  The new cathedral needed to be the envy of the Christian world, the most lavish and magnificent possible.   It would be one befitting Florence’s prosperity, as much about civic pride as religious faith.  

The foundation stone for the new Cathedral of Santa Maria del Fiore was laid in 1296. The original designer and architect was Arnolfo di Cambio, a master mason responsible for other prominent structures in Florence. Although Arnolfo passed away soon after construction began, the project continued, but by 1355, only the cathedral's facade and nave walls existed. Significant progress was made by 1366, including the vaulting of the nave and planning for the east end, which included the dome.  Although Arnolfo had envisioned a dome for the cathedral, no surviving evidence of his original design exists. 

Through the 1300s, the vision for the cathedral kept expanding, but this presented a problem.  Santa Maria del Fiore, like numerous cathedrals, has a cross-shaped layout. As they expanded the church, they also enlarged the crossing or central intersection area where the two arms of the cross meet. The increased size of the church necessitated a larger dome to cover the area over the altar.

Responsibility for building and financing rested with an appointed committee of men known as the Opera del Duomo.  In 1366, at a crucial phase in construction, the Opera requested that the lead architect, Giovanni di Lapo Ghini, begin working on a model for the cathedral's dome. However, the committee also commissioned a second model from a group led by another master mason, Neri di Fioravanti, architect of the rebuilt Ponte Vecchio after its destruction by flood.

Ghini's model followed a relatively traditional Gothic style, featuring thin walls, tall windows, and external buttresses. Buttresses played a vital structural role by supporting the thrust of vaults and allowing for tall walls with numerous windows. Neri’s approach to the dome's structure differed significantly.  In contrast, he rejected the use of external buttresses.    Aesthetic and structural concerns plus political factors may have influenced Neri's decision to reject them. Flying buttresses were rare in Italy as they were considered unsightly and cumbersome by Italian architects, and they were associated with Florence's historical enemies, including Germany, France, and Milan.

Neri proposed a novel and untested idea. Neri believed the dome could be supported without flying buttresses by incorporating stone or wooden chains encircling it, akin to how an iron hoop contains a barrel's staves. This innovation aimed to distribute the dome's stress within its structure, eliminating the need for external support.

The Opera debated between the two models. When Ghini raised concerns about the stability of Neri's design, they compromised. They adopted Neri's model but only by enlarging the pillars supporting the dome. This decision posed challenges, as it affected the planned dimensions of the dome.  A crucial meeting in August 1367 resulted in a wider dome plan than the original.

Overall, Neri's design was groundbreaking. It featured a double-shell dome, a rare feature in Western Europe, with an outer shell for height and weather protection and an inner shell for interior proportions. The dome's profile was pointed, unlike the hemispheric design of most previous cupolas. This unique structure, composed of four interpenetrating barrel vaults, presented unforeseen challenges for the builders who would take on this ambitious project half a century later.  Despite its complexities, Neri's model laid the foundation for the dome of Santa Maria del Fiore as it would ultimately be constructed, and it would call for ingenious solutions during its construction.

Neri's model of the dome became highly revered in Florence. This model, measuring 15 feet in height and 30 feet in length, was displayed in the cathedral as if it were a shrine for a saintly relic.  When Neri died in 1374, construction on the dome had not started, and whatever plans he had for how it was to be constructed died with him.  As of 1418, the dome was still not started.

In 1418, the Opera del Duomo did the most Florentine of things.  They announced a competition to see who could solve the challenges of the dome’s construction.  One of the entrants would be someone familiar to all of Florence, for he had entered another high-profile competition - the one for the Baptistery doors:  Filippo Brunelleschi.

Filippo Brunelleschi was born in Florence in 1377, the son of a notary and civil servant.  His mother was part of the wealthy Spini family. Therefore, they could afford to provide him with a classical, humanist education, which equipped him with a deep understanding of mathematics, geometry, and architecture principles. This education was meant so he could follow his father into civil service. Still being artistically inclined, the young Brunelleschi apprenticed with the Arte della Seta, the silk merchants' guild, the wealthiest and most prestigious guild in the city.   The guild also included jewelers and metal artisans. 

Therefore, he embarked on his career as an apprentice goldsmith.  This path was familiar to many great Renaissance artists such as Donatello and Da Vinci.  During the 15th century, there was no better preparation for a career as an architect, sculptor, or designer. These artisans engaged in the meticulous craftsmanship of working with precious metals like gold and silver. Their pursuits demanded not only manual dexterity but also intellectual acumen. They grappled with the dual challenge of crafting functional objects with aesthetic excellence, requiring them to harmonize practicality and beauty in their creations.

One of Brunelleschi's early groundbreaking achievements was his development of linear perspective. He made significant advancements in understanding how to represent three-dimensional space on a two-dimensional surface. If you wish to learn more about this, you can visit the I Take History With My Coffee blog.  I have included a link in the show notes.  While you are there, check out all the other great historical content.

In 1402, at twenty-one, he emerged as one of two finalists vying for the prestigious commission to fashion new doors for the Baptistery of San Giovanni.  Lorenzo Ghiberti was the other worthy contender, and a peculiar proposition arose: both Brunelleschi and Ghiberti were asked to collaborate on the task.  However, he declined this joint venture for reasons known solely to Brunelleschi.  Consequently, Ghiberti was awarded the commission, and disheartened, Brunelleschi departed from Florence.  

Seeking inspiration and knowledge, Brunelleschi embarked on a transformative journey to Rome.  This is the same one that Donatello accompanied him on.  The ancient Roman ruins that graced the cityscape became his veritable classroom.  After immersing himself in the grandeur of Rome, Brunelleschi eventually returned to Florence.  During this time, he received news of an unprecedented competition that would define his legacy—an opportunity to construct the majestic dome atop the cathedral.

But anyone attempting to construct the dome was met with one particular challenge at the very onset.  The inner dome was to span an expansive area, nearly half the length of a football field, while the outer shell was to rise to a height equivalent to 10 stories above the cathedral walls, which themselves stood at 170 feet tall.  Medieval technology relied on wooden frameworks to hold the masonry until the final piece was put in place. This method is known as "centering."  Yet, such a method was not practical.  The space beneath the dome is exceptionally vast, and constructing the wooden framework necessary to support the masonry would have required hundreds of trees, several years of construction, and substantial funds. 

As far as anyone at the time knew, something like this had never been done before.  So, most of the proposals the Opera del Duomo received depended on wooden centering.  Except for Brunelleschi.  He stepped forward and said he could build the dome without the centering.  The problem was that at age 41, Brunelleschi had not built anything at this point in his life.  The Opera would be choosing him on blind faith.  Naturally, there was some hesitation, and the committee asked him to explain how he intended to do this feat.    Brunelleschi was highly secretive by nature; it was what cost him the commission for the Baptistery doors.  He replied, "I'll show you how to do it when you give me the job. Give me the job, and I'll begin doing it, and you'll see that it works."

Giorgio Vasari relates a story that is, in all probability, a fabrication.  When the committee continued to press Brunelleschi to show them how he intended to build the dome, he told them to bring an egg.  He said that if anyone could stand the egg upright on the table, they would understand his method.  Person after person tried to no avail.  They all demanded Brunelleschi to show them.  He took the egg and, in Vasari’s words, "Pipo rupel cule vovo." "Pipo broke the egg's ass."  Brunelleschi had broken the bottom of the egg.  Everyone protested that they could have easily done that.  Brunelleschi answered, "Yes, and you would be able to build the dome if you know what I know."

In a leap of faith, Brunelleschi was given the job.

To address the challenge of the dome's spread, Brunelleschi adopted Neri’s concept of using stone chains.  Neri never outlined the design of these chains or how they would work within the dome.  This was left to Brunelleschi to decipher.  And he came up with an ingenious solution.  He employed four internal horizontal stone chains embedded within the inner dome. These chains, one at the top, one at the bottom, and two evenly spaced in between, acted like barrel hoops, preventing the dome from deforming due to its octagonal shape. These chains would be done in concentric rings with transverse beams interlocking them.  Imagine railroad ties.  The transverse beams of the bottom chain were horizontal, but on each successive one, they were inclined and rotated like spokes to point to the central hub of the dome.

To ensure their rigidity, the chains were constructed as octagonal sandstone beams, each 43 cm (17 in) in diameter and no more than 2.3 m (7.5 ft) long. They were connected end-to-end with lead-glazed iron splices.  The specifications for the beams and iron clamps were so specialized that they taxed the skill of the artisans appointed to make them.

Hidden iron chains complemented the stone chains, although evidence of these iron chains couldn't be confirmed through a magnetic survey in the 1970s. Brunelleschi also incorporated vertical "ribs" at the corners of the octagon, curving toward the center, each measuring 4 m (13 ft) in depth. These ribs were supported by 16 concealed ribs radiating from the center. They had slits to hold beams, which supported platforms, allowing construction to progress upward without scaffolding.

This presented another problem to be solved.    The challenge was lifting heavy materials, including large stones and building supplies, to great heights with relative ease.  It is said that necessity is the mother of invention.  For this purpose, Brunelleschi invented the ox-hoist.

The hoist featured a wooden frame standing at fifteen feet in height, housing various horizontal and vertical shafts connected through cogged wheels of different sizes.  Its operation was driven by one or two oxen harnessed to a tiller that turned the vertical shaft.  This shaft had two cogged wheels, one at the top and one at the bottom, either of which could engage with a much larger wheel on a horizontal axis. Notably, only one of these wheels on the rotor could be used simultaneously, with one for raising loads and the other for lowering them.  A large screw with a helical thread facilitated the change in gears by lifting or lowering the rotor, allowing it to mesh with the appropriate wheel attached to the largest of the three rope drums.

The screw controlling the rotor's position was an ingenious feature of the hoist, which acted as a clutch to connect or disconnect the gears from the large drum's wheel.  This design enabled the hoist to reverse its operation, lifting or lowering loads without the need to unyoke the oxen and change their direction.  The clockwise movement of the oxen was maintained throughout the process, saving valuable time between each ascending or descending operation.  Oxen were chosen for their strength and endurance but had difficulty walking backward, making this feature highly practical.

Depending on the specific shaft used—small, medium, or large—loads could be raised or lowered.  The differing diameters of these shafts meant that each turned the rope at varying speeds and required varying levels of effort from the oxen.  The largest, with a diameter of five feet, raised loads more quickly than the smallest, which had a diameter of only 20 inches and required more oxen revolutions for each ascent.  The smallest shaft was employed for raising the heaviest loads, similar to a cyclist using the smallest chain wheel for steep ascents.  Using this smallest shaft, a single ox could lift a 1,000-pound load to a height of 200 feet in approximately thirteen minutes.

Brunelleschi left little documentation about his designs behind.  Descriptions of the ox-hoist have come down to us through others, including Leonardo Da Vinci.

Construction of the dome began in earnest in 1420, and by 1425, the building process had reached a critical point.  At this point in construction, the dome walls would start curving inward.  Here, gravity and other stresses play more of a crucial role.  Without the supporting centering framework, how would Brunelleschi keep the entire edifice from collapsing under its own weight?   Brunelleschi had decided he would use brick as the primary building material.  Brick was more lightweight than stone.  A key component of his plan was how the bricks were laid.  

Brunelleschi's construction method involved avoiding a simple arrangement where layers of brick and mortar would be directly stacked on top of each other. This is because such a configuration would create distinct planes of weakness within the wall due to the mortar's lower strength than brick.  Brunelleschi introduced a novel design where horizontal bricks are interspersed with vertically oriented ones. Instead of forming a continuous straight line, the bricks create a zig-zag pattern. This distinctive pattern, known as "spina pesce" in Italian or "herringbone" in English, can still be observed today between the two domes, albeit only in small, unplastered patches.  The vertical bricks block the planes of the mortar's weakness, preventing sheering within the wall.  

But this is not all.  The herringbone pattern starts and then wraps around the corners of the octagon and continues uninterrupted from one facet of the dome to another.  The effect is one continuous spiral.  The spiral resists gravity, preventing cracks, and binds the dome into one unified structure.   The dome is not an octagon, but it is circular. 

On top of this, recently, those studying how Brunelleschi built the dome have hit upon another key ingredient in the brickwork.  The bricks slope down from the corners towards the middle of the walls.  Within each wall, an inverted arch is created.  In tandem with the herringbone pattern, these inverted arches keep the bricks in place and the dome from collapsing.  

The solution to how Brunelleschi achieved this seems to lay in his use of a simple technology - rope lines.  Rope lines are still used today in masonry to ensure accuracy and alignment during construction.  Masons use rope lines to establish precise layout points and guidelines for constructing walls, foundations, and other structures. They determine the starting point and endpoints for the wall, ensuring that it is correctly aligned with the building's design.

On the worker’s platform at the dome’s base, Brunelleschi created a flower pattern to which the ropes would be attached.  As a worker moved the rope along the flower outline, the curve of the flower was translated into the inverted arch of the brickwork.  And to ensure the walls would meet in the center, ropes were crisscrossed to mark the center point.  Before a rope could guide a brick into place, it needed to cross this point.  

Brick by brick, the walls of the dome approached the center.  It would take 16 years of work.  In 1436, the Cathedral of Santa Maria del Fiore was consecrated on the Feast of the Annunciation.  The ceremony was led by Pope Eugene IV and attended by all the important officials of Florence, including Cosimo de Medici.  

Before I close, I want to mention the “uomini senza nome e familia,” "men without name or family," the unskilled workers who carried materials like lime or bricks.  Many laborers came from impoverished families, the popolo minuto.  The construction team included up to 300 individuals, including quarry workers. Life on the building site of the cathedral was challenging and demanding. Workers faced low wages, long hours, dangerous conditions, and inconsistent employment due to bad weather. 

Their workweek extended from Monday to Saturday, often starting at dawn and lasting up to fourteen hours during the summer. The foreman issued payment every Saturday. Some fortunate workers might occasionally be dismissed early, allowing them to purchase food at the nearby Mercato Vecchio. Sundays were designated days of rest, and everything, including work, was prohibited. 

The masons were awakened by church bells throughout the city each working day. They carried their own tools and were expected to maintain and repair them with the help of an on-site blacksmith. Upon arrival at the cathedral, workers recorded their names on a gesso board, similar to clocking in at a factory, and working hours were tracked using sand hourglasses.

A full-time laborer could expect to work approximately 270 days a year on the dome, though weather conditions could reduce this to as few as 200 days. When conditions prevented work on the dome's summit, a lottery system would select five workers to perform tasks like plastering or bricklaying indoors, while the rest of the workforce would be sent home without pay. More extended layoffs were also possible.

The dome of Santa Maria del Fiore is an iconic part of Florence’s skyline.  Today, tourists can mount the very stairs used by the workers during construction.  These stairs lead up to the lantern that caps the dome, and from there, a visitor is rewarded with a spectacular view of Florence and the surrounding countryside.  The dome is a monumental engineering achievement at a time when people had a limited understanding of modern physics and material sciences.   The Florence Cathedral is not just an architectural marvel; it holds immense cultural and historical significance for Florence and Italy. It symbolizes the city's wealth, artistic prowess, and religious devotion during the Renaissance. The dome, in particular, symbolized Florence's cultural and architectural achievements.

I recommend reading Ross King’s Brunelleschi’s Dome.  It is a nicely written yet detailed account of the building of the dome.

In the next episode, we will return to pick up our narrative of the Medici with Cosimo’s grandson, Lorenzo, Il Magnifico.

 
As always, maps and other supporting resources for all episodes are listed in the episode description. In the meantime, for more historical content, please visit the “I Take History With My Coffee” blog at itakehistory.com and also consider liking the I Take History With My Coffee Facebook page.  Feedback and comments are welcome at itakehistory@gmail.com.  Or you can leave a review on Apple Podcasts or on Spotify.  You can also help support this podcast by buying me a coffee at buymeacoffee.com/itakehistory.  If you know anyone else who would enjoy this podcast, please let them know.  And thanks for listening.