by Jim Atkins, FAIA, FKIA
Illustrations by Jim Anderson

Summary: It has been called the greatest accomplishment in Renaissance architecture. Designed and built by Filippo Brunelleschi, a goldsmith, clockmaker, and sculptor turned architect, it remains the world’s largest dome constructed with masonry. And its creation is a story that parallels many of the challenges architects encounter today: competitions, owner sign-offs, client nonpayment, and decisions by committee.

Ultimately, it is a story of triumph, and the end result is an architectural wonder; a classic monument to innovation, invention, perseverance, and dogged determination. It is a story that we architects desperately need as we turn on the lights, crank up the coffee pot, and check on the status of our projects, day after day.

This article is the first in a monthly series for 2008. Each month over the coming year we will return to the 15th century and join Filippo Brunelleschi in his quest to design and build Il Duomo, the magnificent dome of Basilica di Santa Maria del Fiore. We will follow Filippo as he starts out as a goldsmith and sculptor, his explorations in the ancient ruins of Rome, which gave him insight into dome construction, and his successful bid to become a capomaestro, the Renaissance equivalent to the architect of record.

We will follow him as he solves the challenges of masonry constructed without centering, something never before accomplished at this scale. We will observe his development of herringbone-patterned masonry, which effectively transfers loads, allowing the dome to be completed. And we will explore the intricate machines he invented and constructed to hoist and move heavy materials during construction. He truly was a Master Builder.

Yes, our man did just about everything, from hiring and firing workers to an attempt to ship building materials down the Arno River from Pisa in an amphibious barge he designed and built.

He was truly a Renaissance man in that he assumed every role necessary to get the job done, a feat that if pursued today would surely send our insurance agent into cardiac arrest. So settle in for the first episode in this exciting series. You will be amazed at how little the bumps in the road of architecture have changed in the past six centuries. Don’t miss an episode, and you are guaranteed to have a real adventure in architecture.

Monument of the Renaissance: Santa Maria del Fiore
In the late 13th century Florence, Italy was a bustling, prosperous city. The old cathedral in the center of town, Santa Reparata, was too small and racked with age-induced ruin. The city needed a new cathedral, and Santa Reparata was torn down along with adjacent buildings to make room for Basilica di Santa Maria del Fiore, an edifice that would become much more than a church. It would become a symbol of Florentine pride; bigger and better than rival buildings in Pisa and Siena.

The new cathedral was designed in 1296 by Arnolfo di Cambio, a local architect with successful church and civic commissions and an established reputation in Rome. His original design for the cathedral was Gothic, but, by 1366, city leaders followed the advice of local painters and sculptors and made a program change. Apparently, back then, church committees were just as unpredictable as they are today. They decided that all new construction should follow Roman forms, including an octagonal drum supporting a dome that would rest over the intersection of three naves. It would be the largest masonry dome ever built, and it is unparalleled to this day.

Arnolfo had died only six years after construction of the cathedral had begun, and for the next 30 years work almost came to a halt. In 1331 the powerful Arte della Lana, the Guild of Wool Merchants, took over control of operations and put the architect, Giotto, in charge. He would design and build the bell tower. Unions had money and power way back then, and in 14th century Florence the Wool Merchants became the client on the cathedral. They called all the shots. They were the wealthiest and most powerful guild in Europe; bigger than Jimmy Hoffa.

Work continued over the years through multiple architects of record, or capomaestros, including Andrea Pisano; Giovanni di Lapo Chini, who divided the center nave into four square bays; Alberto Arnoldi; Giovanni d’ Ambrogio; Neri di Fioravante; and Orcagna. The cathedral was magnificent, with the exterior walls faced with alternating horizontal and vertical bands of marble in a polychrome red from Siena, white from Carrara, and green from Prato. By 1418, the dome was the only major component remaining to be constructed.

Il Duomo
Arnolfo di Cambio’s original design had no doubt included a dome. His model of the cathedral, however, had long deteriorated and fallen down. Model building is not a new art. It was required by clients during the Renaissance to explain fully the design and scope of the project. Some were as large as small houses. (Plug that into your design budget.) Today, documentation is not available on the original dome as to specifics. It is thought to have been designed for a span of 199 feet, which would have been larger than the existing Santa Sophia in Constantinople.

Nonetheless, a final design began to evolve in 1366 when the wardens of the Opera, the committee administering the work for the Wool Merchants, ordered the current capomaestro, Giovanni di Lapo Ghini, to build a model of the dome.

They also asked another master mason, Neri di Fioravanti, to build a model. Apparently they wanted to reap an optimum result from the minds of the day, and competition was their favorite medium. Architecture was as competitive then as it is now, if not more so.

Giovanni stayed with the Gothic approach with buttresses supporting the drum beneath the dome. Neri, on the other hand, proposed a different design. He proposed that the dome be constructed with tension rings, or chains, that would resist the outward pressures created at the base of the dome, holding the span together like steel hoops hold together the staves of a wooden barrel.

It is interesting that Brunelleschi receives much credit for coming up with the tension ring concept, although he only oversaw their construction. The tension rings were proposed by Neri before Filippo got involved. It affirms the benefits of good public relations and benevolent historians.

The rings would be contained within the walls and thus not visible like the flying buttresses used in Germany and France, a design element that was neither admired nor politically supported by the Florentines. But such a radical design had no precedent, and debate raged among the townspeople and within the Opera del Duomo as to its constructability.

Interestingly, the wardens of the Opera del Duomo eventually chose Neri’s proposal even though the uncertainties of structural design in that day led to great concern. In that time there were many instances of buildings that leaned and some that collapsed entirely. The campanile in neighboring Pisa is the most famous example.

These concerns resulted in the decision to play it safe and enlarge the pilasters within the walls of the drum that supported the dome, thus increasing the overall dome size. The end result was a mean diameter of 143.5 feet. This span surpasses the Pantheon in Rome, making it the largest masonry span in the world. The cathedral’s height would be a record as well, with the lantern and cross above the dome topping out at 375 feet.

Can you imagine receiving a commission for a project with a scope that surpassed all known design and technology? This truly was the greatest accomplishment of the Renaissance, yet such a venture would not have a chance of happening in today’s industry, systemic with lawyers and insurance policy requirements. One message that we must take from this accomplishment is that anything is possible if you have the courage, you have the talent, and you can get the public to support you.

Innovazione
The span of the dome was only one of its remarkable accomplishments. The design required many more innovations to survive as it crept skyward. The absence of scaffolding from the ground, or centering, the dome within a dome construction to reduce loads at the top, the “herringbone” pattern used in the brickwork to direct forces downward instead of inward, and the revolutionary tension rings that provided a structural and aesthetic alternative to the brace-like buttresses, collectively compose this revolutionary and magnificent design.

How did a goldsmith and clockmaker successfully ascend to this lofty level of design accomplishment? Although he did not burn long studio hours in architecture school like the rest of us, he spent untold months and years examining the ruins of ancient Rome to learn from the Romans’ magnificent building technology. He became a student of Roman building technology, magnificent innovations with materials and structures that had been forgotten and buried in the rubble of the Roman Empire.

Perhaps architects today should be required to study the construction of renowned projects as well as their design details and characteristics. If this should happen, perhaps we would experience more projects at the profound level of Brunelleschi.