The biggest masonry dome
Yes, this is not one of the most famous domes in the world, but also the biggest masonry one ever made!
And the surprises are not over! Brunelleschi – Santa Maria del Fiore Dome
ARTIST Filippo Brunelleschi
NAME Dome of Santa Maria del Fiore
LOCATION Santa Maria del Fiore, Florence
YEAR 1420-1436 (1471 with lantern)
DIMENSIONS Internal span 45,5m (149ft), total height 114,5m (376ft)
MATERIAL Bricks and sandstones
Hi everyone and welcome back to Exploring Art with Alessandro!
The dome is considered the creation of a genius, Filippo Brunelleschi, and one of the most important examples of architecture ever built. Well it’s not just for the dimensions (the internal span is 45.5 meters/149ft starting 52 meters/171ft from the ground!) that make it the largest dome ever seen at the time and still the biggest masonry dome in the world, but also for the unique construction techniques that Brunelleschi adopted to build it! Some of them understood after centuries and some of them still unknown!
But let’s go in order 🙂 Brunelleschi – Santa Maria del Fiore Dome
By the beginning of the 15th century, after a hundred years of construction, the Cathedral of Santa Maria del Fiore was still missing its dome! A couple of solutions were suggested, but both had big limits, in particular the use of a centering support.
Centering is normally made of wood timbers, but for a dome starting 52 meters above the floor and spanning 45.5 meters there was not enough timber in Tuscany to build the scaffolding and forms. Moreover, another big issue was that the tholobate or drum got realized on a not precise octagonal base, so without a real center, making the design even more complicated.
In 1418 a contest was supposed to find the man able to finally designed the dome, but design also all the scaffolds and lifting devices pertaining to the construction!
Like in 1401 (read the post about that contest) the finalists were the two rivals Lorenzo Ghiberti and Filippo Brunelleschi. The final design was by Brunelleschi, but they were “forced” to work together until Ghiberti was removed in 1425. The reason of all of that was that Brunelleschi showed his model which it was deliberately incomplete because he was feared someone would copy his designs. When the commission asked how he intended to make the real dome he refused further explanations and he started to be mocked.
According to Vasari (the most important biographer at that time) Brunelleschi 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.“
The commission did not trust him completely and Ghiberti (who was really appreciated and famous in Florence) was asked to work with him.
The works started in 1420 and actually Brunelleschi showed to know exactly what to do.
Building the dome
The dome could not be semicircular because:
- it was not possible to use centering,
- thrust issues and
- it was necessary to build the dome from the 8 sides of the base.
Brunelleschi designed a dome with a higher curvature and actually formed by 2 shells: an inner and an outer one to cover the first.
Both shells were supposed to be built by bricks for 2 reasons: the lighter weight compare to stone and because Brunelleschi could not use a central support system and he needed to position the bricks in a specific way so that the walls were able to support themselves.
The solution was to lay the bricks in a herringbone pattern which spiraled to the top of the dome with vertical bricks acting his bookends to hold the others in place.
They laid about one roll a week giving the mortar time to cure. But it is amazing to think how it was possible to reach such high elevation with that perfection without the modern tools we can use today! Even more difficult if we consider that the two shells have different thickness that decrease based on the height!
The shells are held together by giant brick vertical arches and horizontal ribs and interlocking rings of stone. The rings, called also chains, are very important because they act like barrel hoops keeping the dome from expanding outward and collapse! There are four stone chains built like an octagonal railroad track with parallel rails and cross ties, all made of sandstone beams 43 centimeters (17 in) in diameter and no more than 2.3 meters (7.5 ft) long. A fifth chain, made of wood, was placed between the first and second of the stone chains.
In 1436, after 16 years, the dome was completed, but not like we know it today: the lantern in fact was added starting from 1446, few months before Brunelleschi death. Brunelleschi designed the octagonal lantern with eight radiating buttresses and eight high arched windows too not only for aesthetic reasons, but in particular to make the structure more resistant and solid. The lantern in fact, with its heavy weight of about 750 tons, helps to push the thrusts along the eight external ribs.
The lantern was finally completed by Brunelleschi’s friend Michelozzo in 1461. On the top it was crowned with a gilt copper ball and cross by Verrocchio in 1469. This brings the total height of the dome and lantern to 114.5 meters (376 ft).
Even now, after centuries, many of the methods used by Brunelleschi are still not fully understood. A modern understanding of physical laws and the mathematical tools for calculating stresses were centuries in the future.
So Brunelleschi had to rely on intuition and whatever he could learn from the large scale models he built, but also on his studies of the ancient architectures. These elements combined made him a genius who changed architecture enhancing culture and emotions! Brunelleschi – Santa Maria del Fiore Dome