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During our first trip to Italy, we spent 3 days in Florence. Out the window of our home base, Hotel De Lansi, was the main church of Florence, The Basilica of Saint Mary of the Flower. The ideas and architectural techniques used to build its dome played an important role in igniting the Renaissance.
Florence’s Duomo is the largest masonry brick dome ever constructed. It was begun in 1296 in the Gothic style under the design of Arnolfo di Cambio and completed in 1436 with the dome engineered by Filippo Brunelleschi. The architectural decision in 1367 to reject traditional Gothic buttresses was one of the first events of the Italian Renaissance. The change from Medieval Gothic to a classic Mediterranean dome signaled a return to the early knowledge of the Romans. When completed, the huge building had a length of 502 feet, width of 124 feet, width at the crossing of 295 feet, height of the arches of 75 feet, and height of the dome of 375.7 feet.
After 100 years of construction, the dome was still missing. The original design called for an octagonal dome higher and wider than any ever built. It was to have no external buttresses to keep it from spreading and falling under its own weight. On August 18, 2023 a structural design competition for erecting Neri’s dome was started. The two main competitors were Lorenzo Ghiberti and Filippo Brunelleschi. Ghiberti had won the competition for a pair of bronze doors for The Baptistery in 1401. Brunelleschi was a goldsmith and clockmaker with no formal architectural training. With the support of Cosimo de Medici, Brunelleschi won the commission.
Brunelleschi looked to the Parthenon in Rome for inspiration and solutions to his complex design problems. Its dome was a single shell of concrete. A wooden form had held the Parthenon dome aloft while its concrete set. The formulas and architectural secrets for its design were long gone. Filippo’s challenge was even greater. He had to find a way to build a dome without a temporary wooden supporting frame. The masonry brick had to hold itself up with nothing underneath.
He also had to figure out how to keep the dome itself from spreading out and falling under its own weight. The mathematical tools for calculating all the stresses required a genius that we are still trying to figure out centuries later.
Some of the amazing ideas and inventions that he used included- 1.The 8-sided dome had an inner and outer shell of sandstone and marble that were interlocked with stone and wood. No one knows where he got the inspiration for that idea. 2. The spreading problem was solved by a set of four internal horizontal stone and iron chains serving as barrel hoops embedded within the inner dome. One was at the top, one at the bottom, and 2 spaced evenly in between. Since the dome was octagonal, a single chain squeezing the dome like a barrel hoop put all the pressure on the 8 corners of the dome. 3. The masonry brick had to support itself. To accomplish this he precisely placed the bricks in a herringbone pattern. This transferred the weight of freshly laid bricks to the nearest vertical ribs of the non-circular dome. Progress was slow because he had to let the bricks dry before he moved upward. His calculations worked because each face of the dome met perfectly at the top. 4. He invented massive lifting device driven by oxen that hoisted over 37,000 tons of material, 4,000,000 bricks and many large stones.
The decoration of the exterior was not completed until 1887. They are faced with alternate vertical and horizontal bands of polychrome marble from Carrara(white), Prato(green), and Siena(red). Recently there was a special on PBS produced by Nova and National Geographic called “Solving the Mysteries of the Duomo”. Check it out to understand more secrets revealed about this architectural genius.
www.duomofirenze.it/index.eng.htm
www.travel-to-florence.com/duomo-museum.html
February 21, 2023
