Brunelleschi's Dome
by Ed Buch, CSI, CCS, AIA

Is it possible that one of the largest brick and mortar domes ever constructed was built in the Renaissance and done so by hand? Brunelleschi’s Dome: How a Renaissance Genius Reinvented Architecture, by Ross King (Penguin Books, 2000, 194 pages), tells the rich history of the dome on the Cathedral of Santa Maria del Fiore in Florence, Italy.

You may recall from your art history class that Santa Maria del Fiore was constructed next to the Baptistery where Lorenzo Ghiberti’s famous bronze doors, “The Gates of Paradise” are located. In fact, Filippo Brunelleschi lost the competition to design and cast the doors to his bitter rival, Ghiberti. In the competition for the design and construction of the dome on the cathedral, the outcome was reversed and Filippo won.

Filippo Brunelleschi was a goldsmith and watchmaker by training. In 1418, at the age of 41, he won the competition with a truly revolutionary design that allowed the dome to be constructed without wooden centering. The dome is immense, being 143 feet in diameter, larger than St. Paul’s in London or St. Peter’s in Rome. It is also taller than the Gothic cathedrals that preceded it. The base of the dome was 140 feet above the cathedral floor and it soared another 170 feet to the cupola at the top. It was literally a towering achievement in Renaissance architectural design and construction. Filippo would spend the next 38 years working on the dome, dying in 1446, shortly before it was finally completed.

The dome’s structural system began with a series of 8 vertical ribs that met at the cupola forming a pointed framework. The dome was not a true semicircle in either plan or in section, as many before it had been. The masonry infill between the vertical ribs was laid up by hand, course by course, with each new course extending inward to form the dome. The secret to resisting the horizontal outward thrust at the base of the dome was a series of timber and stone “chains”. These were concealed within the two shells of the dome, the outer shell being on average about two feet thick and the inner shell averaging about six feet in thickness.

The description of the structural system and the complicated brickwork would have benefited greatly by the inclusion of a few drawings. It is very difficult to picture the complicated, three dimensional brickwork described. Drawings would also have been useful to understand the oxen powered hoisting equipment used to deliver the thousands of tons of masonry and stone from the floor of the cathedral to the dome. Filippo designed and built this equipment himself.

The wool merchant’s guild of Florence, that raised the funds to pay for the dome and selected Filippo to execute it, really made a leap of faith when they chose him. Consider that they selected someone without any construction experience, someone who proposed a design that had never been used before, that the design was not based on a structural theory or calculations, and that the only thing they had to go on was a scale model mock up. This is an example of the “trial and error” method of construction that was the standard practice of the day. Many building did fail as a result.

The fact that the dome was a success was a significant factor in raising the status of architects who, up to the Renaissance, had been considered by society as craftsman rather than artists. In summary, the book is a fascinating story of 15th Century Italy, of Brunelleschi as a person, and of his dome.

Ed Buch is an architect in the Los Angeles office of Leo A Daly. A Nebraska native, he has worked in Los Angeles since 1988. Prior to that, he worked in Omaha and Lincoln, Nebraska, and 5 years in Riyadh, Saudi Arabia. He has been member since 1981, and is currently an Institute director from the West Region, CSI.