IT HAPPENED TODAY 7 AUGUST 1420: WORKS FOR THE CONSTRUCTION OF THE MOST ORIGINAL DOME IN THE WORLD START IN FLORENCE: THE BRUNELLESCHI DOME
In theory, the famous “Brunelleschi’s dome” should not be there because the original project of the Florence Cathedral (dedicated to Santa Maria del Fiore) provided for a different architectural solution for covering the focal point of Christian cathedrals: the junction of the cross drawn from the nave main and from the transept.
The construction site of the cathedral was opened at the end of 1294 and the base of the “drum”, the architectural element connecting the body of the cathedral and the dome, was already ready in 1314.
But at the beginning of the fifteenth century, 90 years later, the tambour is still waiting for a cover no one has found the architectural solution because the problem of what exactly is located above this structure. It is probable that this unfortunate impasse is not to be attributed to the great architect Arnolfo di Cambio but to the onset of serious and unexpected stability problems deriving from the static load that should produce a traditional round dome, that is, with an arched profile. semicircular, with dimensions suitable for the bulk of the cathedral.
Arrived in the year 1418, 123 years after the opening of the construction site, the Opera del Duomo, the body established in 1296 responsible for the management of the works, is forced to announce a new specific public competition for a project expressly dedicated to the future dome. As a result of the competition, the two architects Filippo Brunelleschi (1377-1446) and Lorenzo Ghiberti (1378-1455) were appointed “supervisors”. On 7 August 602 years ago, work began on the most original dome in the world.
Three years later Ghiberti was expelled from the construction site and the direction of the works passed entirely to Brunelleschi.
Brunelleschi’s project-program was so detailed that, in the installation, there were already the anchor rings which, once Brunelleschi’s program was so detailed that, in the installation of frescoes necessary for the execution of the interiors. Unfortunately Brunelleschi will not be able to see his completed work because he died in 1446, six years after the beginning of the works. But the staff will carry out with great diligence the project and program drawn up by the famous Florentine architect.
At the end of the works, the dome will have a diameter of 45.5 m and a height of about 34 m with the “lantern” on top, a 21 m white marble tower.
Years later, in 1471, the gilded copper sphere with an upper cross was installed on the lantern, created by Andrea del Verrocchio, the artist famous for having opened the most artistic workshop-school of all time in Florence. Leonardo Da Vinci, Sandro Botticelli, Perugino, Ghirlandaio and many others are trained.
With the Verrocchio sphere the total height from the ground reaches 116 m.
The truly innovative element of Brunelleschi’s work is the “self-supporting” dome, a self-cohesive structure that does not require special support structures, such as large pillars that unload the weight on the ground. This solution is obtained through an ingenious engineering masterpiece: the static interaction between two coaxial external domes, one internal, which acts as a support and a brilliant, covered with tiles, the one we all see. The gap between the two domes is about 1.20 m.
In this way the total load of the structure is divided between the self-supporting capacity of the external dome, that of the internal dome and the drum, which responds to the tensions towards the outside. A static load splitting that vaguely recalls the load charge used in modern multi-stage rockets in which each insurance stage has its own thrust and is released when it has used up its fuel quota without burdening in the subsequent phases of the.
The fundamental stylistic feature is the octagonal plan of the external dome, which unloads directly on the drum, which is also octagonal; the aesthetic result is eight converging dynamic “sails” that join at the base of the lantern.
It should also be considered that a very pronounced discontinuous “segmented” dome is even more difficult to fresco internally; with the double dome Brunelleschi has also solved this problem.
A further stylistic element that contributes to global harmony is the observance of the so-called “golden proportions”, ie precise numerical ratios between the main linear parameters of the work.
If you go to Florence do not miss to admire the famous breathtaking view of Fiesole; what allows you a global view of the city and admire “from above” the emergence of Brunelleschi’s jewel.
For those who love to deepen: “The secret of Brunelleschi’s dome in Florence”, by Giuseppe Conti; Publisher Pontecorboli.