The dome of the Cathedral of Santa Maria Del Fiore in Florence, Italy was built and completed in 14386 by a genius mastermind Filippo Brunelleschi. It is known for its supple curves and innovative engineering. The making of this dome is till the date a huge mystery, as no one can exactly figure out it’s making.
Filippo Brunelleschi was a hot-tempered goldsmith who created the most miraculous edifice of the Renaissance! Let’s dive into the article to know more about the revolutionizing architecture and construction of the Brunelleschi Dome.
The Florence Cathedral named Santa Maria del Fiore was a 1296 medieval era cathedral built amongst numerous churches, public buildings and houses constructed with Romanesque or Gothic architecture. Built with pointed arches and angular vertical spaces, the cathedral was one of the prime buildings of the city of Florence. Structurally completed by Filippo Brunelleschi in 1436, with the addition of the dome, the exterior of the basilica is faced with polychrome marble panels in various shades of green and pink, bordered with white and has an elaborate 19th century Gothic Revival façade by Emilio De Fabris.
A monumental problem ignored for decades was addressed by the town fathers in 1418. The problem was a massive hole in the roof of the cathedral. The only possible solution to this problem was to build a dome nearly 150 feet wide and 180 feet above the ground on the top of the existing walls. This dome was going to be the largest masonry dome ever built! But who would take up the challenge to build a masonry dome with such a massive scale with hardly any construction technology and technique in the 15th century?
Other questions revolving around the problem were – Could a dome weighing tens and thousands of tons stay up? Was there enough timber in Tuscany for the scaffolding and templates that would be needed to shape the dome’s masonry? And could a dome be built at all on the octagonal floor plan dictated by the existing walls – eight pie-shaped wedges – without collapsing inward as the masonry arced toward the apex? No one knew.
To address the problem, a competition was organised with architects and engineers across the world giving their proposals and inputs to the problem as the methods of how the dome should be constructed. Amongst those architects and engineers, there was one hot-headed goldsmith who was what the town fathers called “a buffoon and a babbler”.
This hot-headed goldsmith was Filippo Brunelleschi. He promised to build not one, but two domes with one nested inside the other. He claimed this to be done without an elaborate and expensive scaffolding.
The next year the overseers met with Brunelleschi several times, eliciting more details of his scheme. They began to realize just how brilliant (and risky) it really was. His dome would consist of two concentric shells, an inner one visible from within the cathedral nested inside a wider, taller external dome. To counteract “hoop stress,” the outward, bulging pressure created by a large structure’s weight that could cause it to crack or collapse, he would bind the walls with tension rings of stone, iron, and wood, like hoops on a barrel. He’d build the first 46 feet in stone, he said, after which he would continue with lighter materials, either spugna or brick. He also assured the overseers that he could do without conventional, ground-based scaffolding. They welcomed the enormous savings in lumber and labour that would result, at least during work on the first 57 feet, after which everything would depend on how things went, “because, in building, only practical experience will teach that which is to be followed.”
The mastermind behind the largest masonry dome in the world was none other than a goldsmith from Florence, Filippo Brunelleschi. He later was called the father of Renaissance architecture due to his notable contributions to the renaissance architecture and his noble achievement of ‘Linear perspective’
As a boy, during his goldsmith’s apprenticeship, he had mastered drawing and painting, wood carving, sculpture in silver and bronze, stone setting, niello, and enamel work. Later he studied optics and tinkered endlessly with wheels, gears, weights, and motion, building several ingenious clocks, including what may have been one of the first alarm clocks in history. Applying his theoretical and mechanical knowledge to the observation of the natural world, he single-handedly worked out the rules of linear perspective. He’d just spent several years in Rome measuring and sketching the ancient monuments and noting, in cypher, their architectural secrets. Indeed, Brunelleschi’s life seemed to have been one long apprenticeship for building the dome of unequalled beauty, usefulness, honour, and power that Florence yearned for.
The architecture of the Brunelleschi Dome
The structure of the dome is a double-shell structure consisting of an inner dome as well as an outer dome. Both the pillars are supported by sturdy pillars. This practice was successively followed in many domes including Les Invalides of Paris and the United States Capitol in Washington. This protected the inner dome from rain by the outer dome and allowed a higher and more majestic form. The frame of the dome is composed of twenty-eight horizontal and vertical marble ribs, or, eperoni, eight of which are visible on the outside. Those visible on the outside are largely decorative since the outer dome is supported by the structure of the inner dome. A narrow stairway runs upward between the two domes to the lantern on the top.
In contemplating this masterpiece, it is noticed that the builders have made use of balance and harmony between each of its parts. Each architectural element contributes to the stability of the dome as it stands without supporting structures. Another of these crucial elements is the lantern, on top of which rests the bronze ball built by Verrocchio in 1472. To position the ball, they used machines invented by Brunelleschi. The young Leonardo da Vinci figured among the apprentices that helped in this difficult operation.
High up on the fresco in the dome, around the cupola, hovers a temple with the twenty-four elders of the Apocalypse; beneath this, on terraced registers, follow choirs of angels with the instruments of the Passion; groups of saints; personifications of the gifts of the Holy Spirit, of the virtues, and of the beatitudes; and finally, the regions of hell with various deadly sins. The composition of the fresco thus takes into account the architectonic form of the vault in its eight sections, hard upon one another. These frescoes can be seen very well on the way up to the dome.
The work on the dome, the lantern and the exedra occupied most of the remainder of Brunelleschi’s life. Brunelleschi’s success can be attributed to his technical and mathematical genius. Brunelleschi used more than four million bricks in the construction of the octagonal dome. Notably, Brunelleschi left behind no building plans or diagrams detailing the dome’s structure; scholars’ surmise that he constructed the dome as though it were hemispherical, which would have allowed the dome to support itself.
Geometry and Constructive Techniques
From a structural point of view the Brunelleschi’s Dome consists of two layers: an inner thin dome spanning the diameter of the octahedral ring beam and an external thin one to protect it against the environmental loads (Fig. 1). The inner layer (intrados) has a constant thickness; the outer layer (extrados) becomes gradually thinner from the base to the oculus. These two layers are structurally connected by masonry joining elements that start from the octahedral ring beam and continue until the oculus, the top level of the Dome. The whole structure of the Dome was built by Brunelleschi without formwork, the circular profiles of the ribs and rings seems to be maintained by a system of measuring wires fixed at the centres of curvature. The method used by Brunelleschi to build the (polygonal) Dome without the use of a supporting framework, was to complete each of the masonry rings that compose the dome in succession. Before closing each ring of bricks, the workmen placed a row of bricks whose longer sides protruded with respect to the bricks resting on the conic surface. This arrangement, known as a herring-bone (“spina di pesce”), displays a spiral profile. The function of the spiral herring-bone arrangement of the bricks is to make possible to “block” the masonry courses as they were built. The bricks are thus prevented from slipping away as a consequence of the steep inward slope of the masonry beds.
Second feature of the construction is represented by the characteristic profile of the brick beds, known as “slack line” (“corda blanda”) as they resemble a loose string. The reason for this is that the brick beds all lie on the surface of an inverted cone whose axis coincides with that of the dome. Then the cone’s vertex shifts upwards as the work proceeds. This immediately created problems as its size prevented the traditional method of construction.
The first problem to be solved was purely technical: no known lifting mechanisms at the time were capable of raising and manoeuvring the enormously heavy materials he had to work with, including sandstone beams, so far off the ground. Here Brunelleschi outdid himself.
He invented a three-speed hoist with an intricate system of gears, pulleys, screws, and driveshafts powered by a single yoke of oxen turning a wooden tiller and the Castello, a 65-foot-tall crane with a series of counterweights and hand screws to move loads laterally once they’d been raised to the right height.
The octagonal shape of the dome is definitely inspired by that of the Baptistry. The whole structure of the dome is designed to be light and slim in both form and substance. In fact, from an octagonal drum of the dome stand eight segments, the sails, arranged on two shells separated by a space. Brunelleschi wove regular courses of herringbone brickwork, little known before his time, into the texture of the cupola, giving the entire structure additional solidity.
Brunelleschi’s dome still rises from the terra-cotta sea of Florence’s roof tiles, itself terra-cotta clad yet harmoniously proportioned, like a Greek goddess in homespun. It is mountainous yet strangely buoyant, as if the white marble ridges rising to its apex are ropes holding a zeppelin to Earth. Somehow Brunelleschi captured freedom in stone, exalting the Florentine skyline ever after with an upward-yearning embodiment of the human spirit.
The dome is a masterpiece of beauty and engineering, a pioneering construction for its time, and in many ways remains unmatched. As a master of illusions, Brunelleschi was known in Florence to have made people believe in things that did not exist. The construction of its dome sparked years of debate on what was the “magic trick that provided the result that lay in front of everyone, i.e., how the octagonal dome was able to stand! Even today, although extensive studies have been carried out and many new discoveries have been made, there is still a debate on what was the ingenious solution found by the architect Filippo Brunelleschi.
No one was able to develop a workable plan for building a dome nearly 150 feet across that would have to rest 180 feet above the ground on top of the existing walls, which were built to form an approximate octagon without a true centre. No one was certain if a dome could be built at all over the octagonal floor without allowing the masonry to collapse inward as it arced toward the apex. Moreover, the architecture prevented the use of traditional Gothic flying buttresses and pointed arches familiar to builders working at that time.
Almost 600 years ago after it was built, Filippo Brunelleschi’s dome of Santa Maria del Fiore in Florence, Italy, remains the largest masonry dome ever built. Leaving no plans or sketches behind, some of the secrets of its construction that Brunelleschi pioneered are still an enigma today.