The Duomo or the Santa Maria del Fiore: Brunelleschi’s Dome

Brunelleschi portrait Brancacci chapel

We head up via one of the crossing pillars and walk towards the lantern in between the two shells of the dome.  Along a staircase situated on the inner dome wall, we arrive at the lantern where we are given a beautiful view over the city of Florence with its many red roof tiles.

space between the shells and the
staircase on the inner shell
Youtube climb to the top
Santa Maria del Fiore Duomo dome stairs space between the shells
dome and the lantern
Youtube  Duomo google 3
dome lantern Santa Maria del Fiore Duomo Florence Brunelleschi

pictures: auggie tolosa

Videos Brunelleschi and the construction of the dome:

1.  YouTube Duomo google 3
2.   YouTube construction of the dome National Geographic (3. 49 minutes)
3.   YouTube construction of the dome National Geographic (51.55 minutes)
4.0 YouTube building the dome Srinivasan Sadasivam (Vol-I)
4.1 YouTube construction of the dome Srinivasan Sadasivam (Vol-II)
4.2 YouTube construction of the dome Srinivasan Sadasivam (Vol-III)
4.3 YouTube construction of the dome Srinivasan Sadasivam (Vol-IV)
5.    YouTube Khan Academy dome Brunelleschi (5.51 minutes)
6.   YouTube the old and new hoisting method of Brunelleschi
7.0 Youtube The Godfathers of the Renaissance  (complete 55.21 minutes)
7.1 YouTube  part I Brunelleschi (9.49 – 22.20)
7.2 YouTube  part II Brunelleschi (25.52 – 27.20)
7.3 YouTube  part III Brunelleschi (45.50-50.47)
8.   YouTube Brunelleschi as inventor of the perspective (starts at 2.20 minutes)

Arnolfo di Cambio had always intended to cover the enormous space of some 45,50 metres with a dome.5  The problem was that no one really knew how to place a dome over such a wide space.

Santa Maria del Fiore
under construction
Santa Maria del Fiore Duomo under construction

In 1366, the board of the Opera del Duomo orders the construction of two dome models. One is a quite traditional design by master building Giovanni di Lapo Ghini. The other model, which would end up winning, was by a group surrounding Neri di Fioravanti. Di Lapo Ghini’s model was based on the aerial arches and buttresses that were commonplace in Gothicism. This wasn’t particularly popular in Italy. Quite a number of Italian architects saw aerial arches as a rather ugly aid. What was remarkable about the winning model is that it was not being supported by aerial arches. And, quite unusually so, the dome would become double-walled. Fioravanti’s model was deemed the best during a referendum. The model was placed in the aisle of the Duomo for quite some time and after Brunelleschi had built his dome it became a urinal. Despite Neri di Fioravanti’s model, no one really knew how to build that kind of dome. On 19th August 1418, the ‘construction firm’ wrote down the following problem:

‘Whoever desires to make any model or design for the vaulting of the main dome of the Cathedral under construction by the Opera del Duomo  — for armature, scaffold or other thing, or any lifting device pertaining to the construction and perfection of said dome or vault — shall do so before the end of the month of September.  If the model be used he shall be entitled to a payment of 200 gold Florins’

Cited from: Frank D. Prager et al, ‘Brunelleschi: Studies of His Technology and Inventions’, 2012, p. 27

Contenders included Filippo Brunelleschi and Lorenzo Ghiberti.These two artists had been competitors before when trying to land the assignment for the doors of the Baptistery. Vasari, but also Brunelleschi’s biographer, Antonio Manetti, delve into the affairs of these rivals and the construction of the dome. The design of Brunelleschi was revolutionary as he wanted to construct the double-walled dome without centring.

Santa Maria del Fiore Duomo under construction Brunelleschi

Centring is a type of falsework: the temporary structure upon which the stones of an arch or vault are laid during construction. After the cement dried, a process that often took many months, the wooden construction was removed. The shape of the dome would ensure the stones would support themselves. Ghiberti, who lacked experience and knowledge of complicated constructions, insisted on using centring. No one had ever constructed a vault without wooden falsework. Let alone a dome that spanned some 45,5 metres. Another issue is that Fioravanti’s old model of some 50 years prior lacked the semi-dome shape that you would see at the Pantheon, for instance. The arch didn’t have to be semi-round, but a bit pointed: the quinto acuto arch (pointed fifth). This was an extra handicap. How would they ever construct it without centring (the tholobate alone was nine metres high) at a height of fifty-two metres? Vasari gives a detailed account of the meeting where the commission wanted to reach a decision on what model to construct:

‘By the year 1420, all these ultramontane masters were finally assembled in Florence, and likewise those of Tuscany and all the ingenious craftsmen of design in Florence; and so Filippo [Brunelleschi] returned from Rome. They all assembled, therefore, in the Office of Works of Santa Maria del Fiore, in the presence of the Consuls and of the Wardens, together with a select body of the most ingenious citizens, to the end that these might hear the mind of each master on the question and might decide on a method of vaulting this tribune. Having called them, then, into the audience, they heard the minds of all, one by one, and the plan that each architect had devised for that work. And a fine thing it was to hear their strange and diverse opinions about the matter, for the reason that some said that piers must be built up from the level of the ground, which should have the arches turned upon them and should uphold the wooden bridges for sustaining the weight; others said that it was best to make the dome of sponge-stone, to the end that the weight might be less; and many were agreed that a pier should be built in the center, and that the dome should be raised in the shape of a pavilion, like that of San Giovanni in Florence.  Nor were there wanting men who said that it would have been a good thing to fill it with earth mingled with small coins, to the end that, when it had been raised, anyone who wanted some of that earth might be given leave to go and fetch it, and thus the people would carry it away in a moment without any expense.  Filippo alone said that it could be raised without so much woodwork [Teg: required for the scaffolding and centring], without piers, without earth, without so great expenditure on so many arches, and very easily without any framework.’

Giorgio Vasari, ‘’Lives of the Artists’, Filippo Brunelleschi Part 2 : The dome for the Cathedral of Florence (original edition 1568).

Santa Maria del Fiore
without dome
Santa Maria del Fiore without dome Duomo Florence
Brunelleschi scaffolding for the construction of the dome
Duomo Brunelleschi scaffolding for the construction of the dome

The commission responded in disbelief. They immediately asked how Filippo Brunelleschi intended to do this. Brunelleschi, who always feared someone would copy his designs, refused further explanation, but according to Vasari he said:

‘[…] Dear sirs, please understand that the dome cannot possibly be constructed in any other way, and while you may mock me, you will understand that this is the only way, should you refrain from stubbornness, that this dome will be built.’

Brunelleschi only received more mocking laughter and was forcefully removed from the hall. According to his biographer Manetti: ‘He had a feeling they said behind his back:   ‘Look at that crazy man, talking such rubbish.8

Brunelleschi dome

The idea of Pippo, as Filippo Brunelleschi was often called, might have seemed crazy at first, but it would yield enormous benefits if it could be performed. Vasari describes how Pippo managed to persuade the commission during a second meeting in the same year by using an egg. Brunelleschi, with one egg in his hand, walked forward and challenged people into trying to place the egg upright on a marble plate without it toppling over. He who would succeed, would construct the dome.

 Giuseppe Fattori
Brunelleschi’s egg
 Giuseppe Fattori Brunelleschi's egg

After some laughter of those present, some of them gave it a shot but of course failed miserably. Until Brunelleschi walked forward with confidence, picked up an egg, tapped it onto the plate and whilst it was broken on the bottom, it none the less stood upright. Those present exclaimed that if they knew that was allowed, they’d have done the same thing. Filippo answered cleverly:  “if you looked at my model and design, you would also be able to build the dome.9

The commission finally yielded, according to Vasari, and they granted him the assignment for the dome. It’s quite likely that this egg story isn’t completely factual. Manetti makes no reference to this story in his biography about his friend Brunelleschi. What is for certain, however, is that Filippo Brunelleschi’s model would be carried out.

 wooden model dome and exedras
Museo dell’ Opera del Duomo
wooden model dome and exedras Museo dell' Opera del Duomo

Unfortunately for Filippo, the assignment would not be without obstacles, revealing that the clients were not entirely reassured:

  • much to his shock, his arch rival Lorenzo Ghiberti was named capomaestro alongside him.
  • not using the centring would apply only for the first thirty braccia, or 17.5 metres (1 bracchio is 58.36 centimetres; derived from an arm length).

After the first thirty braccia of the pointed dome, the curvature became sharper: sixty instead of thirty degrees at the start of the dome. At reaching a height of 17.50 metres, they would re-examine how to mason the remaining 14.40 metres. YouTube about the hazardous curving

One of the biggest issues faced by Brunelleschi was how to get the massive marble bricks and sandstone up to a height of fifty-two metres. Careful estimations would place the weight at some thirty million kilos. For this purpose, Brunelleschi developed a clever hoist driven by oxen. What was unique about it is that it enabled a swift transition from upward movement to downward movement, while the oxen simply continued their path in one direction, clock-wise.10 In addition, weights up to seven-hundred kilos were hoisted up effortlessly. Later, Brunelleschi developed another hoist that could lift large and heavy beams in all directions and accurately place them, too: the castello, see YouTube.

YouTube: Brunelleschi’s revolutionary method
YouTube castello

Brunelleschi drawing hoist Duomo Florence

A twelve-page document, likely by Filippo Brunelleschi himself, accurately describes how the dome was to be constructed.11   There was consensus about two things ever since the model of 1366 by Neri di Fioravanti.

1. The dome had to be double-walled.
2. The forces were not to be absorbed by gothic-style support arches, but by rings and chains in the dome walls.
ribs between the two shells
Brunelleschi dome Duomo ribs between the two shells

The three exedras did function as buttresses, but they looked much nicer than the usual gothic cross brace system. The latter (point 2) means that the required support to stop the outward force was kept from view.

exedra dome Brunelleschi Duomo

The two walls of the dome were raised simultaneously.12 There were eight masonry shifts; one working at each side of the octagon. Heavy marble ribs were placed on the corners of each side: eight in total. Another two ribs were placed between the two walls on each plane, creating a total of 24. The inner wall started at the tholobate, with a diameter of 2 metres, but down to 1.5 metres near the top. The outer wall began sixty and ended at thirty centimetres. Like in the Pantheon, heavy materials were used at the base of the dome wands and lighter materials including pumice at the top. This was done to reduce the pressure put on the dome.

lifting and bricklaying
dome Duomo Santa Maria del Fiore lifting and bricklaying Florence

By implementing a chain of heavy sandstone, but some made of wood as well, into the wall surface, the dome was kept in place and the gigantic horizontal forces were kept in check. The two rows of chains were supported by hardstone beams in the same way sleepers carry rails.13

chain of heavy sandstone
chain of wooden beams
dome Brunelleschi Duomo chain of heavy sandstone chain of wooden beams 

This can still be seen on the outside of the dome (lower right). The nine rings that move horizontally have a similar function as the sandstone chains. The corner ribs, the ribs between the shells and the many connecting arches keep the two walls firmly together.

Dome construction
1.  Outer shell
2.   Inner shell
3.   Ribbs
4.   Ribs between shells
5.   Ribs between shells
6.   Non-elastic stone chain
7.   Second stone chain
8.   Thirdecond stone chain
9.   Elastic wooden chain
10. Horizontal arches
11. Oculus
four of the protruding beams of the first stone chain
The irons were meant for
‘the crow’s nest’ designed by Baccio d’Agnolo
never completed as per Michelangelo’s advise
four of the protruding beams of the first stone chain Dome Duomo Brunelleschi

wooden chain between the shells
stone chain

Brunelleschi dome Duomo wooden chain between the shells

The brickwork was proceeding nicely. One problem was that after each walled layer, the builders had to wait for the cement to harden; after all, they did not use scaffolding and each horizontal layer had to support itself.

Building pace of the dome: 1422  (start) and 1426
1426, 1433, 1436 (up to the lantern)

Vasari, but Manetti too, describe how Brunelleschi eliminated his rival Lorenzo Ghiberti as fellow capomaestro.14

One day, Brunelleschi reported in sick and stayed in bed. Work was halted. Ghiberti had no idea what to do and provided vague answers to masons who wanted to know how to continue. The board went towards Brunelleschi’s home and pleaded for him to continue work as the masons were all stuck. That is how it became known who was the expert and who wasn’t. Later on, it became evident that Ghiberti does a sloppy job at constructing the stone chain. His rival, needless to say, endeavoured to make this fact public. Ghiberti played his part as well. Brunelleschi was arrested for not being a member of the masonry guild, which was in violation with the laws of that time. Presumably, Ghiberti or one of his friends was behind this. By interference of the board, Brunelleschi was soon released. Lorenzo Ghiberti wrote an angry letter to the board of the Opera del Duomo, blaming Brunelleschi for not adhering to the old model by Neri di Fioravanti. The letter ended with …

‘This is the result of the inadequacy and arrogance of those tasked with its construction; those who are being paid and rewarded fairly. I write this now in case the inevitable occurs and the building is ruined and becomes derelict, so that I shall go free of blame. My dear sirs, be cautious, but I am sure you will be. Consider the dangers faced by the Siena cathedral, before trusting a dreamer without clarity of thought.’

‘This is the result of the inadequacy and arrogance of those tasked with its construction; those who are being paid and rewarded fairly. I write this now in case the inevitable occurs and the building is ruined and becomes derelict, so that I shall go free of blame. My dear sirs, be cautious, but I am sure you will be. Consider the dangers faced by the Siena cathedral, before trusting a dreamer without clarity of thought.’

Cited from [Dutch]: Ross King, ‘De koepel van Brunelleschi’, de Bezige Bij, Amsterdam, 2002 p. 111.

But the board did trust the dreamer: Filippo. His miraculous hoists left a great impression. In fact, Filippo Brunelleschi ultimately received the responsibility for the project and Ghiberti had to settle for a far lesser role. The masonry type used by Brunelleschi, herringbone, was not entirely novel. Romans had used it before, but for decorative purposes only. What is new is that Filippo used vertical stones, with the next stone joining horizontally, to anchor the nine horizontal rings and make them sturdier. What’s more, the downward force is absorbed much better this way (see YouTube at HD history).15

expansion Museo dell’Opera del Duomo
excavations in parking garage and the discovery of the herringbone pattern brickwork in the dome

expansion Museo dell'Opera del Duomo excavations in parking garage and the discovery of the herringbone pattern brickwork in the dome.

In 2012, during the expansion of the Museo Opera dell’Duomo, an important discovery was made. A small dome was discovered in a parking garage during the excavations.

YouTube of the discovery
dome with herringbone masonry type
Brunelleschi dome with herringbone masonry type discovered in 2012

The revolutionary masonry patterns in the dome of the Duomo were used here as well. Brunelleschi presumably built this to convince the commission, but also the masons that this type of masonry would produce sturdy walls.

harringbone brickwork
along the edge between the north and north-east segments
uncovered during restauration work on vault
Duomo dome harringbone brickwork along the edge between the north and north-east segments uncovered during restauration work on vault

A vertically placed brick is less resistant against the downward force of the stone mass than a horizontally walled brick.

Giovanni di Prato
Giovanni di Prato 1426 Dome Santa Maria del Fiore

Brunelleschi did not leave any documents detailing the construction of the dome. Nonetheless, a parchment document was uncovered with a drawing and text by Giovanni di Prato. This document, written five years into the construction of the dome, has Giovanni providing an account of the rope lines and what they were attached to. Brunelleschi used the ropes to accurately check each of the eight walls so they would line up perfectly at the top. In the text next to the drawing, Giovanni presents a sharp critique of Brunelleschi and he predicts the dome will collapse. See also the video about the rope lines and the drawing with text by Giovanni Di Prato.

The dome was completed in 1436, but the octagonal opening at the top still needed its crown.

Day one continuation 2