Filippo Brunelleschi: The dome of Santa Maria del Fiore.

The Florence Cathedral (Santa Maria del Fiore), with Brunelleschi’s Dome, the nave, and Giotto’s Campanile as seen from Michelangelo Hill (Florence, Italy).

In Florence, the influence of this group of artists and scholars with humanistic ideals began to be felt in all social classes, and as architecture is the most readily available art for society, people wished the appearance of something new in monumental art. This explains why in 1420 an artist full of enthusiasm, young and not yet known (but whose love for antiquity was very notorious), was entrusted with the most important work to be executed in Florence at that time: the finishing of the cathedral by means of a dome projected on top of its crossing. In Vasari’s book “Lives of the Most Excellent Painters, Sculptors, and Architects“, he tells us a multitude of anecdotes about the dome’s architect, Filippo Brunelleschi (1377 – 15 April 1446): his trips to Rome to study architectural problems, a meeting of architects from all over Italy and even from abroad in order to propose a solution, and finally, a kind of contest, imposed collaborations with old masters, and a thousand other difficulties that Brunelleschi initially encountered in order to develop his plan with total independence.

Everything described by Vasari reflects the truth, and it was documented that until 1423 Brunelleschi was named inventore e governatore della cuppola maggiore; but the truth is that the first directors of the architectural works for the cathedral of Florence had to necessarily conceive some type of dome or octagonal tower to close the area occupied by the transept. Vasari makes us believe, with the meeting of these foreign masters in a kind of symposium, as if they hesitated between finishing the cathedral with a dome or with an octagonal tower, like those of the old monastic churches and Gothic cathedrals. But it is unquestionable that the first architects who designed the floor plan of Santa Maria del Fiore already thought of constructing a dome, which would be somewhat larger than those of the cathedrals of Pisa and Siena. The difficulty of building Santa Maria del Fiore‘s dome resided precisely in its different magnitude. Although the domes of Pisa and Siena, like that of Florence, covered the width of the three naves, their diameter was much smaller; the diameter of the dome of Florence would reach 40 meters and, therefore, would impose a colossal thrust, much more difficult to counter act than that of the domes of Pisa and Siena.

The dome of the Florence Cathedral was still missing in the beginning of the 15th century, even after a hundred years of construction. An initial design for the dome was proposed by Arnolfo di Cambio in 1296 and called for an octagonal dome higher and wider than any that had ever been built, with the particularity of no external buttresses to keep it from spreading and falling under its own weight. The following architects and builders of the cathedral aligned with the commitment to reject the use of traditional Gothic buttresses when Neri di Fioravanti’s model was chosen in 1367. This architectural choice was one of the first events that marked the beginning of the Italian Renaissance, by signaling a break with the Medieval Gothic forms and a return to the classic Mediterranean dome. Additionally, the use of buttresses was forbidden in Florence. Neri’s model depicted a massive inner dome, open at the top to admit light, like Rome’s Pantheon, but enclosed in a thinner outer shell, partly supported by the inner dome, to keep out the weather. This dome had to rest on an unbuttressed octagonal drum. In the absence of external buttresses or other type of structural external support, Neri’s dome would need an internal defense against spreading under its own weight, but no one had came with a design yet as the building of such a massive masonry dome posed many technical problems at the time.

Aerial view of the Pantheon of Rome (Rome, Italy).

Until recently it had been accepted without discussion, the idea proposed by Vasari, that Brunelleschi went to look for inspirations to tackle this difficult challenge by studying the ancient Roman domes, and that along his travels to study ancient ruins he had found the secret of building the dome according to the system of the ancient Romans. This theory was excellent for flattering Roman art and made Brunelleschi’s work to appear converging to the nascent movement that aimed to restore the forms of antiquity. Brunelleschi looked to the dome of Rome’s Pantheon for solutions. In fact, the Pantheon of Rome was cited as the structure that served as model for the design of Florence’s dome; but the similarity between the two domes rests only in their dimensions: both have almost the same diameter. In addition, the Pantheon has a concrete dome that supports its hemispherical shell on the huge cylindrical walls in which it rests; instead, the dome of Florence had to be risen above the church and was raised even higher because it rests on an octagonal drum, thus the structure of the dome itself stands mostly in the air. Their construction is also different: the dome of the Pantheon is a massif of concrete and brick (but the formula for concrete had long since been forgotten), while the dome of Florence is a shell of sandstone, marble and brick. For the construction of the Pantheon, ancient Romans employed structural centring to support the concrete dome while the concrete cured. In the case of a dome the size of that of Florence (designed by Neri starting 52 meters (171 ft) above the floor and spanning 44 meters (144 ft) in diameter), there was not enough timber in Tuscany to build the scaffolding and the necessary inner falsework. Brunelleschi followed Neri’s initial design and envisioned a double shell, made of sandstone and marble. For the dome itself, Brunelleschi chose brick, due to its light weight compared to stone, and with nothing under it during its construction. To illustrate his construction proposal, Brunelleschi constructed a wooden and brick model with the help of Donatello and Nanni di Banco, a model which is still displayed in the Museo dell’Opera del Duomo in Florence.

Brunelleschi’s architectural model for the dome and tribunes of Santa Maria del Fiore (Museo de ll’Opera del Duomo, Florence, Italy).
Illustration showing the inner structure of Brunelleschi’s dome as it was being built.

Brunelleschi’s dome subdivides its weight (in order to exert less thrust) by means of a lower inner dome and an outer dome that, raised in a pointed arch, serves as a buttress to the inner dome. Indeed, due to the weight exerted from their center, hemispherical domes tend to sink so that their edges open outwards; instead, pointed domes tend to open at their cusp and, consequently, their edges exert great inward thrust (opposite to the hemispherical domes). By combining them both, Brunelleschi managed to counteract the horizontal thrust exerted by the hemispherical dome with the weight, in the opposite direction, exerted by the outer dome with a pointed profile. This was Brunelleschi’s most ingenious invention which must have been inspired by medieval models; certainly, it was the same system used in the Cistercian Romanesque domes which, being spherical inside, are placed inside a higher square or octagonal tower that appears as an outer dome; but that also, by means of its weight, acts as a vertical force, deviates the thrust of the dome, and acts as a buttress.

In addition, Brunelleschi also solved the problem of the outward stress exerted by the dome, by securing (strengthening) the inner dome with large rings of wooden beams joined together with iron bars serving as barrel hoops embedded within the inner dome: one at the top, one at the bottom, with the remaining two evenly spaced between them. A fifth chain, made of wood, was placed between the first and second of the stone chains. Since the dome was octagonal rather than round, a simple chain, squeezing the dome like a barrel hoop, would have put all its pressure on the eight corners of the dome. Each of these horizontal stone chains was built like an octagonal railroad track with parallel rails and cross ties, all made of sandstone beams. These rails and cross ties were notched together and then covered with the bricks and mortar of the inner dome.

 

Illustration showing the structure of Brunelleschi’s dome with the structural ribs.

Brunelleschi also built vertical ribs springing from the corners of the octagonal drum, curving towards the center point. These main ribs, 4 metres (13 ft) deep, are also supported by 16 additional concealed ribs radiating from the center. The ribs had slits to take beams that supported platforms, thus allowing the work to progress upward without the need for scaffolding. This combination of the dynamic system of the Middle Ages and the static system of antiquity is what constitutes the true innovation of the dome of Florence. Brunelleschi also introduced the idea of building the dome without using a falsework, with only a light wooden castle (scaffolding) so that the workers could work; the dome closed as it was being built from base to top, and it gave itself support. This seems to be what caused the most surprise at the time of its building. Leon Battista Alberti, in his book Della Pittura (“On Painting”) dedicated to Brunelleschi, says with Tuscan exaggeration: “Who before you, Filippo architect, dared to build structure of such dimension, upright towards the sky, wide to cover with its shadow all Tuscan people, and executed without the help of falsework or woodwork with such artifice that, if I understand it well, it seems as incredible to those of now as it was ignored by the ancients? ”

 

Brunelleschi’s dome seen from the interior of the Cathedral. The frescoes represent The Last Judgment and started in 1568 by Giorgio Vasari and Federico Zuccari, they were finished by 1579.

Brunelleschi, like all cathedral builders of those times and before, had to rely on intuition and whatever he could learn from the large scale models he built. To lift tons of material for the construction, he invented hoisting machines and lewissons for hoisting large stones. These specially designed machines and his structural innovations were Brunelleschi’s chief contribution to architecture. Although for the construction of Florence’s dome he was executing Neri’s design made half a century earlier, it is his name, rather than Neri’s, that is commonly associated with the dome. But what gives value to Brunelleschi’s dome is not only its engineering or magnitude, but its beauty. Vasari, writing a century later, still reflects the amazement of the Florentines when they saw it standing so beautiful over their city. “It” he says “seemed like a new hill that had been born in the middle of the houses; the graceful Tuscan hills of the surroundings recognized it immediately as their sister”. This indicates the admirable harmony of this architectural work with its surrounding environment, it could only be Florentine. It is one of the most universal works that humanity has ever built, concealing its volume by the subtle gesture of its profile and a natural elegance that only Florence could produce. With its slightly pointed shape placed on the octagonal drum, with its simple circular windows, the severe color of its tiles and the beautiful marble lantern on its top, the dome of Santa Maria del Fiore is still today what most characterizes the skyline of Florence.

Brunelleschi’s dome seen from the Giotto’s Campanile. Notice the cross ties of the bottom stone chain that can be seen protruding from the drum at the base of the dome. These stone chains (4 in total) were used to strengthen the inner dome.

Brunelleschi didn’t see the dome finished, although he dedicated almost his whole life to this great construction. In 1420 he began to direct the works and only until 1446 the first stone of the lantern (which was also designed by him) was laid, he died few months later. The lantern was finally completed by Brunelleschi’s friend Michelozzo in 1461. The conical roof was crowned with a gilt copper ball and cross, containing holy relics, by the sculptor Andrea del Verrocchio in 1469, whose young apprentice at the time was Leonardo da Vinci. Fascinated by Brunelleschi’s machines, which Verrocchio used to hoist the ball, Leonardo made a series of sketches of them and, as a result, is often given credit for their invention. The lantern, together with its crowning, brings the total height of the dome to 114.5 metres (376 ft). Until today, the dome of Santa Maria del Fiore is still the largest masonry dome in the world.

The dome’s crowning lantern, also after a design by Brunelleschi.

Naturally, Filippo Brunellescchi was buried in the Cathedral. On his grave, Il Buggiano (his adopted son) sculpted a portrait that is an artistic equivalent to the phrase Vasari wrote: “Fu Filippo facetissimo nel suo ragionamento e molto arguto nelle risposte …” (“Filippo was very easy in his reasoning and very witty in his answers”). The stories we know of this first Renaissance architect are beautiful and told, in addition to Vasari’s book, in other contemporary writings such as those by Antonio Manetti, his biographer. From their reading we can learn that Brunelleschi, most skilled in all the arts, abandoned them all for his dominant hobby, architecture. The group of Florentine artists and writers of the first half of the 15th century felt a limitless admiration for the master director of the dome. And Brunelleschi was worthy of the praise that the artists of his time placed on him and of the respect and admiration he received by successive generations: the dome of Florence is one of the few monuments that since its construction has been unanimously considered as perfect, despite the changes in taste and style from era to era. To raise the dome of Florence, Brunelleschi contributed with his studies of Roman antiquities, medieval domes and perhaps the Byzantine domes of Ravenna, and with these elements, put together brilliantly, he produced an original work in all senses.

The tomb of Filippo Brunelleschi in the crypt of Santa Maria del Fiore. The fact that the architect was allowed to be buried in such a prestigious place as is the grounds of the Cathedral is a proof of the high esteem Florentines had for the artist.
Death mask of Filippo Brunelleschi by Il Buggiano (Museo dell’Opera del Duomo, Florence).

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Centring: A type of falsework. The temporary structure upon which the stones of an arch or vault are laid during construction. Until the keystone is inserted an arch has no strength and needs the centring to keep the voussoirs in their correct relative positions. Centring is normally made of wood timbers.

 

Concrete: A composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. In the past limebased cement binders were often used, such as lime putty. The cement reacts with the water and other ingredients to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. Because concrete cures (which is not the same as drying such as with paint) how concrete is handled after it is poured is just as important as before. Concrete is one of the most frequently used building materials.

Lewisson: (Also known as a “lewis”). A category of lifting devices used by stonemasons to lift large stones into place with a crane, chain block, or winch. It is inserted into a specially prepared hole in the top of a stone, directly above its center of mass. It works by applying principles of the lever.

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