Brunelleschis Dome (7 page)

Even if sufficient numbers of good-quality trees could be found, and even if the expense of sawing the wood and assembling the vast structure could be absorbed, other problems would have confronted the wardens. The act of decentering — the removal of the wood from beneath the finished vault — was one of the most hazardous operations in the entire building process. During the Middle Ages the most usual method of decentering was to set the supporting poles of the center’s scaffolding in sand-filled kegs and then, at the time of striking, to unplug the kegs and allow the sand to escape, thereby slowly lowering the level of the wooden framework. This operation may seem simple, but timing was a major problem. Medieval mortars remained “green” for up to a year or even eighteen months, until the water necessary for crystallization had completely evaporated. The centering for the vaults of the south tribune, for example, remained in place for thirteen months, from June 1420 until July 1421, thus tying up a large amount of timber that could have been reused elsewhere — for example, in the loading platform for the cupola. If centering was struck too early, the mortar would still be plastic and its strength insufficient. On the other hand, long-term loadings create a deformation of wood known to engineers as “creep”: if the centering was left in place for too long, the timber would warp beneath the weight of the vault it supported, causing the masonry to shift. This phenomenon was known to the ancient Greeks, who would remove the wheels of their chariots at night, or else prop the chariots vertically against a wall (as Telemachus does in Book IV of the
Odyssey
) in order to prevent the wheels from warping under the weight of the stationary vehicles.

A final difficulty was that the centering for such a massive dome would have been awkward and obtrusive, even when erected in an area as large as the cathedral’s central octagon. Vast in scale, running from the ground to the oculus — the open window at the top of the dome — it would have crowded the octagon and left little room for the masons to maneuver.

One design for the dome’s centering existed already, a legacy of Giovanni di Lapo Ghini, the
capomaestro
whose plan for the cupola had lost out to Neri di Fioravanti’s. His wooden model of the centering, executed in 1371, sat inside Neri’s 1367 model. But evidently this model, like that of Giovanni d’Ambrogio, was inadequate to the task.

By the end of August, barely two weeks into the competition, Filippo had already begun building a brick model of the cupola. The wardens of the Opera appointed four master masons to assist with its construction. They must have been taken aback by what they saw, perhaps suspecting Filippo of preparing a clever illusion like his painting of the Baptistery, one that would deceive the senses and defy the laws of reason. As with his panel, Filippo set about his task with meticulous craftsmanship. For the woodwork he had hired two of Florence’s most gifted sculptors, his friend Donatello and also Nanni di Banco, the son of the late
capomaestro
and a man who had worked on the cathedral for over ten years. The four masons sent from the Opera spent a total of ninety days working on the model.

Constructed in one of the courtyards of the Opera, Filippo’s model was the size of a small building, requiring forty-nine cartloads of quicklime and over 5,000 bricks. It had a span of over six feet and stood twelve feet tall, easily high enough for the wardens and various consultants to walk inside to inspect it. And like many architectural models it must also have been an exquisitely rendered work of art, for the carvings by Donatello and Nanni di Banco — two men whose brilliantly lifelike sculptures adorned the facade and side portals of the cathedral — had been gilded and painted by the artist Stefano del Nero.

Although the competition was originally intended to end on September 30, it was extended by two more months, perhaps to allow Filippo to complete his elaborate model, or to give some of his rivals, masters from Pisa and Siena, time to transport themselves and their models to Florence. Not until December 1418 did a Great Council consisting of the thirteen wardens along with consuls of the Wool Guild and various consultants assemble in the nave of the cathedral to consider the various designs. After bread and wine were served, the models were discussed. Filippo’s brick model in particular received a good deal of attention, both on December 7 and then two weeks later, when its merits were debated over a period of four days.

The documents of the Opera del Duomo record these bare facts and nothing more. But Filippo’s two biographers, Manetti and Vasari, relate a livelier tale. Despite assurances in the original proclamation of August 1418 that all models would find a
bene et gratiose audietur
— a “friendly and trustworthy audience” — Filippo’s proposal was greeted by the wardens and its chosen experts with skepticism and even, at times, outright hostility.

The reasons for these reactions are not difficult to understand. Filippo had approached the problem of the centering in a revolutionary manner, one utterly different from his rivals’. Everyone else took it for granted that an elaborate framework would be required to support the masonry of the rising dome; the only questions were ones of economics and design. One of the proposals put forward involved sustaining the cupola on a temporary mound of earth piled to a height of 300 feet. This project is not actually as ridiculous as it might sound, since Romanesque vaults were sometimes built over rooms that had been filled with earth. Indeed, as late as 1496, soil heaped to a height of 98 feet was used as a centering for the vaults in the cathedral at Troyes. But the proposal was met with derision in the Great Council. One of the wardens suggested, with withering sarcasm, that coins should be mixed into the dirt so that when the time came to decenter the immense vault, the citizens of Florence would be eager to lend a helping hand.

Filippo, on the other hand, offered a simpler and more daring solution: he proposed to do away with the centering altogether. This was an astounding proposal. Even the smallest arches were built over wooden centering. How then would it be possible to span the enormous diameter called for in the 1367 model without any support, particularly when the bricks at the top of the vault would be inclined at 60-degree angles to the horizontal? So astonishing was the plan that many of Filippo’s contemporaries considered him a lunatic. And it has likewise confounded more recent commentators who are reluctant to believe that such a feat could actually have been possible.
³

Filippo did himself few favors when he appeared before the Great Council to expound his revolutionary design. Anxious, as usual, that no one should steal the fruits of his ingenuity, he stubbornly refused to divulge to the wardens the explicit technical details of his plans. The wardens, naturally, were little impressed by this sort of coyness. They pressed Filippo to elaborate. He refused. So heated did the exchanges become, according to Vasari, that he was first derided as “an ass and a babbler,” then physically ejected from one of the more unpleasant assemblies. Many years later he would confide to Antonio Manetti that he had been ashamed to show his face in the street for fear of being taunted as “that madman who utters such nonsense.” His ingenious plan looked like a lost cause.

Filippo was naturally incensed by this treatment, and the experience served to confirm his low opinion of what, ten years later, he would call “the ignorant crowd.” But in Florence, as Vasari notes, no one’s opinion remains unchanged for long. Just what won the wardens round to the merits of Filippo’s project is unclear. Vasari relates an anecdote that is as amusing as it is improbable — a legend like that of Archimedes in his bathtub or Newton under the apple tree. In this parable Filippo suggests to the wardens that whoever can make an egg stand on end on a flat piece of marble should win the commission. When all of the other contestants fail the test, Filippo simply cracks the egg on the bottom and then stands it upright. When his rivals protest that they might have done the same, Filippo retorts that they would know how to vault the cupola, too, if only they knew his plans. And so the commission, Vasari claims, promptly went to Filippo.

It seems unlikely in the extreme that the serious-minded wool magnates of the Opera del Duomo would be tempted to hand over the commission on the basis of such a parlor trick. Implausible as the story sounds, however, it is worth noting how the humble egg has long fascinated scientists and engineers. Both Alexander of Aphrodisia and Pliny the Elder marveled at the longitudinal strength of this apparently flimsy structure that, as the latter states, “no human force can break.” Galileo, too, would ponder the phenomenon. In a fragment dedicated to his son he inquires, “Why is it that an egg held with your hands by its top and bottom and pressed with great force cannot be crushed?” His pupil Vincenzo Viviani resumed the topic, going so far as to speculate that the egg — or, rather, a half eggshell, placed upside down — was the inspiration behind the architecture of the domed vault.

The egg anecdote aside, the results of the deliberations by the Opera were not as clear-cut and decisive as Vasari implies, though in December 1418 most of the other models were indeed eliminated from consideration. The panel of judges fixed their attention on the two remaining designs, one of which would be selected as the basis for the dome’s construction. History had begun repeating itself. The first model was, of course, Filippo’s. The second, also made of brick, and also built in one of the Opera’s courtyards, had been designed by his old adversary, Lorenzo Ghiberti.

T
HE PREVIOUS SIXTEEN
years had treated Filippo’s fellow goldsmith very well. At the age of forty, Lorenzo Ghiberti had become one of the most renowned artists in all of Italy. He was bald like Filippo but, unlike Filippo, looked merry and avuncular, with a moon face and a large, fleshy nose. As was the custom in Florence, he had married late, at the age of thirty-seven, taking as his bride a sixteen-year old, Marsilia, the daughter of a wool comber, who promptly gave him two sons. Most of his time was spent in his workshop opposite the convent of Santa Maria Novella, where, after almost two decades of work, he was still busy casting the doors for the Baptistery in a giant, purpose-built furnace. Thus far he had melted almost 6,000 pounds of bronze for the project.

Lorenzo was a prosperous man by now, with a house in Florence and a vineyard in the country. As his stepfather Bartoluccio had prophesied in 1401, he was no longer required to make earrings for a living. Since winning the competition for the Baptistery doors, he had been kept busy with commissions: tombs in marble or bronze, candelabras, shrines, reliefs for the baptismal font in Siena Cathedral, and a bronze statue of St. John the Baptist for the Guild of Cloth Merchants. Completed in 1414 and installed in a niche at Orsanmichele, this statue, at almost nine feet tall, was the largest work in bronze ever cast in Florence — a testament to Lorenzo’s ambition and skill.

But Lorenzo, for all of this work, had precious little experience as an architect. Indeed, his model for the cupola marks his first foray into that field. In contrast to Filippo’s, his model was neither large nor intricate. His four masons worked only four days each on it, compared with the ninety spent on Filippo’s. It was made from
mattoni picholini
, or small bricks, and presumably involved some sort of centering, for Lorenzo also employed a carpenter in its construction.
¹
This was probably the fundamental difference between the two models that the wardens found themselves obliged to choose between.

The flurry of activity in the last months of 1418 was followed by a lull of more than a year. No firm decisions were made. Christmas arrived: the wardens ordered geese for themselves. On New Year’s Day, as usual, they swore their oath to build the dome according to Neri di Fioravanti’s model. Then for a number of months they dithered and delayed. The cupola project languished. No one — neither Filippo nor Lorenzo — was awarded the prize of 200 florins.

One of the reasons for the delay was that a crack had been discovered in the vaulting of the north tribune. This vault had been raised little more than ten years earlier, so its fracture was hardly an auspicious sign under which to begin raising an enormous and structurally uncertain cupola. Another reason was that old Giovanni d’Ambrogio had been removed from his post as
capomaestro
, having become too decrepit to ascend to the top of the vault to inspect the work of the stonemasons. A third reason was that, one month after the Great Council, events temporarily overcame the cupola project: in January 1419 Pope Martin V and his entourage arrived in Florence.

Martin V had been elected pope several years earlier at the Council of Constance, which ended the Great Schism, the 39-year period in which the Roman Catholic Church was divided between rival popes in Rome and Avignon. The council had deposed John XXIII, a one-time pirate and dedicated libertine who was said to have seduced hundreds of women, and replaced him with Martin. The new pope would remain in Florence for the next twenty months, until Rome could be properly fortified and some of its churches restored. In the meantime Florence had to be made hospitable for His Holiness. The Opera del Duomo therefore diverted masons and carpenters from the cathedral to Santa Maria Novella, where a sumptuous set of apartments was hastily contrived, complete with a staircase that the Opera commissioned from Lorenzo after a competition involving two other designs. This verdict must have augured well, in Lorenzo’s mind, for the Opera’s other, much larger commission.

Filippo bided his time fruitfully during these months. He refined his model, adding both a lantern and a circular gallery around the drum. But by now he, like Lorenzo, was involved with other projects. The year 1419 was, for him, an
annus mirabilis
of sorts. In the six months following the cupola competition he received four separate architectural commissions, all in Florence. This is remarkable in light of the fact that he had won no prior commissions. It suggests that, for all the ridicule to which they were subjected, his plans for the dome had won him a good deal of respect.