Brunelleschis Dome (15 page)

These various safety measures appear to have worked: after the two deaths in the south tribune in the summer of 1420, only one other fatality is recorded, that of a mason named Nenno di Chello who fell to his death in February 1422 It is an almost miraculous safety record considering the number of men employed, the perilous nature of their work, and the many years the project took to complete.

Another hazard faced by the masons was unemployment. As the shells rose and the circumference gradually narrowed, fewer bricks needed to be laid, and therefore fewer masons were needed. Twenty-five of them were sacked in April 1426, though in this case the redundancies may have resulted from a labor dispute. Manetti claims the master masons “selfishly unionised themselves” — an act contrary to Florentine law — and went on strike for higher pay. Conflict over working conditions may also have played a part in the strike. Such strikes were not unknown in Florence, where the all-powerful guilds were reluctant to extend liberties to the workers upon whose toils their own prosperity depended. The previous century had seen strikes, secret meetings, rock-throwing crowds, the beginnings of workingmen’s associations, even full-scale insurrections.
⁴
The most famous example of the latter was the so-called Ciompi uprising of 1378, when the city’s downtrodden cloth workers revolted against their masters and, amid mass disturbances, set fire to the palaces of the aristocratic families and temporarily seized control of the Republic.

No such revolution was permitted to erupt at Santa Maria del Fiore. Filippo responded in ruthless fashion, promptly sacking the masons and hiring Lombards to replace them — the strikebreaking technique beloved of later opponents of trade unions. Finding themselves unemployed, the dismissed masons humbly petitioned Filippo for the return of their old jobs. Vasari, who also tells the story, gleefully reports that Filippo did indeed rehire them, but on lower salaries,“so instead of getting something more, as they thought they would, they suffered a loss, and in venting their spite on Filippo they injured and disgraced themselves.”
⁵

It is safe to assume that the masons, like the stone cutters and ironmongers, were initially puzzled by what the
capomaestro
required of them. It comes as no surprise that the brickwork in the shells was as complex and inventive as everything else Filippo designed for the cupola. The bricks were not merely laid in horizontal layers: at regular intervals in both shells the rings were interrupted by larger bricks laid on their ends — that is, at right angles to the horizontal courses. This angled brickwork is the
spinapescie
(fishbone) bond mentioned in the 1426 amendment. These vertical bricks, each of which passed through four or five horizontal rings, ascended in diagonal bands to the top of the dome, forming a zigzag or herringbone pattern. Filippo must have known that these spiraling bands of upright bricks would constitute planes of weakness, since they were less able than a more conventional bond to counter the hoop stresses that threatened to crack the dome.
⁶
Why, then, should he have chosen to use the herringbone bond?

Herringbone brickwork.

The reason behind Filippo’s choice of this pattern lies in the particular structural behavior of arches and domes. A dome is built on the principle of an arch, whose stones, as we have seen, are kept in place by mutual pressures brought into play by their own weight. Once complete, each of them is under circumferential compression and therefore, like an arch, becomes self-supporting. But the problem in constructing a dome arises from the fact that these rings cannot be built instantaneously. Some form of temporary support is therefore needed until the rings are complete because, until they are closed, the tendency of the masonry is obviously to fall inward.

Filippo used the herringbone bricks to counter this tendency. The upright bricks projecting from the horizontal courses served as what one of the cathedral’s
capomaestri
, Giovanni Battista Nelli, surveying the cupola over two hundred years later, called
morse
,“clamps.” From his observations Nelli realized that Filippo had adopted a different pattern of brickwork at the level of the second sandstone chain, as the masonry began curving inward, and that this pattern had helped to hold in place the surrounding horizontal bricks as the mortar cured. Every three feet or so, these upright bricks interrupt the horizontal courses, subdividing each new layer into shorter sections roughly five bricks long. While under construction, the short sections were connected by the upright bricks to several completed layers beneath. Each row of five bricks, that is, was locked into position by the vertical bricks on either side. These acted rather like bookends, keying the new layer to the completed, self-sustaining ones beneath.

The incomplete courses of bricks were therefore held in place not by an internal support (as in the case of a wooden centering) but by a pressure applied from either side. Even before the ring was complete and the mortar had cured, the short sections of bricks were transformed into self-contained horizontal arches capable of withstanding the inward pull of gravity. The herringbone pattern, an ingenious system used by Filippo as part of his technique to do away with the need for an elaborate centering, is therefore essential to the dome’s structure. In
On Architecture
Alberti later describes this technique as being essential for building a vault without centering, because connections bind the weaker components to the stronger ones. He compares the result to the human body, in which Nature “joins bone with bones and binds the flesh with tendons, introducing connections in all directions in length, breadth, depth and slantwise.”

Where exactly Filippo learned of the herringbone bond is one of the dome’s unsolved mysteries. The pattern had of course been known to masons and bricklayers for many centuries. The Romans made extensive use of the bond they called
opus spicatum
, and the pattern is also found in the half-timbered brick walls of Tudor houses in England. In both these cases, however, it is decorative rather than structural; indeed, the Romans used it only in ornamental paving on the floors of their villas.
⁷

Slightly farther afield, systems of interlocking brickwork similar to that in the cupola in Florence can be found in certain Persian and Byzantine domes, leading some scholars to speculate that Filippo may have visited these lands. This hypothesis is not improbable given the trade link with Asia Minor (which was so well known to Italians as early as the thirteenth century that Marco Polo did not consider it worth describing) as well as Filippo’s many “lost years” between 1401 and 1418. He may also have gained secondhand knowledge of these domes from merchants returning from the East or even, possibly, from the many Muslim slaves in Florence. No wealthy family in Florence could do without at least a couple of these “domestic enemies” (as Petrarch called them), among whom were found Turks, Parthians, and Chaldeans, all from the Near East.
⁸
Still, the majority of these slaves were adolescent girls, and their familiarity with Seljuk vaulting techniques must have been scanty.

Having inspected the dome’s brickwork, Nelli was confident that the method could be applied elsewhere, daring to envision other such enormous structures. “Operating in this manner,” he wrote, “any massive curved structure can be raised from the ground to any height whatsoever without support from centering or scaffolding.” The dome of another of Filippo’s designs, Santo Spirito, was built in this way, and Antonio da Sangallo the Younger made use of it in the next century. But the full magnitude of Nelli’s claim has never been tested except at Santa Maria del Fiore. This is for the simple reason that no masonry dome larger than Filippo’s great cupola has ever been constructed.

T
HE BOOK OF
G
ENESIS
tells us that after the Flood, when everyone on earth still spoke the same language, some of the descendants of Noah traveled east into the deserts of Babylonia, in modern-day Iraq. Hoping to make a name for themselves, these new inhabitants of Babylonia took it upon themselves to found a great city named Babel, “the gate of God”: “And they said, Go to, let us build us a city, and a tower, whose top may reach unto heaven.”

The rest of the story is well known, of course. It is a parable of the ambitious pride of mankind and, more specifically, of architects. Using kiln-baked bricks mortared together with tar, the people of Babel built an edifice that rose to an incredible height. But the tower was never finished. Angered by man’s attempt to reach the heavens — to build beyond his assigned station on earth — the Lord confounded the tongues of the builders so that no one could understand anyone else’s speech. Not surprisingly, the ambitious project ended prematurely and unhappily.

Modern commentators speculate that the story of the tower of Babel is an attempt by the ancient Hebrews to account for the enormous, half-ruined ziggurats, or stepped pyramids, that had been raised by the Sumerians, the world’s oldest civilization. The story also seeks to account for linguistic diversity, for we learn that after abandoning their tower, the Babelites with their myriad new languages were dispersed across the face of the earth, giving rise to new nations, each with its separate tongue. But the story is likewise an architectural version of the Fall of Man. The attempt to reach the heavens, and therefore to rival God, recalls Adam and Eve’s ambition to gain forbidden knowledge in the Garden of Eden. The great tower — a would-be bridge between man and God — becomes an architectural equivalent of the Tree of Life, which likewise would have erased the difference between the Creator and his creatures.

Buildings of large dimensions have always posed moral problems.
¹
A number of Roman authors disapproved of excessively large edifices either because of their lack of utility or because of the tremendous expenditure involved in their construction. Plutarch, for example, condemned the enormous baths and palaces of the emperor Domitian, and both Pliny and Frontinus vehemently rejected the Seven Wonders of the World, which the former regarded distastefully as a foolish display of wealth on the part of kings. By contrast, the aqueducts maintained by Frontinus, though immense, served the important purpose of bringing fresh water to the citizens of Rome.

In the twelfth century, the Cistercian abbot Bernard of Clairvaux condemned the vast height of the new Gothic churches that were rising everywhere across France. Such suspicions can also be found in the writings of Leon Battista Alberti, who attacks the pyramids in the same critical vein as Pliny and Frontinus, claiming that the “monstrous” works of the Egyptians were an “insane idea.” In light of this pronouncement, his positive estimation of the dome of Santa Maria del Fiore (one of whose virtues, he claims, is its sheer scale) comes quite unexpectedly:

What man, however hard of heart or jealous, would not praise Pippo the architect when he sees here such an enormous construction towering above the heavens, vast enough to cover the entire Tuscan population with its shadow, and done without the aid of beams or elaborate wooden supports?

The reference to the dome’s all-encompassing shadow may be an allusion to the pyramids of Egypt, which were said to cast shadows as long as a journey of several days.
²
Alberti justifies the gigantic dimensions of the dome because they reveal both evidence of man’s God-given power to invent and the superiority of Florentine commerce and culture. Filippo and his masons even appear to have succeeded where the architects of Babel failed, for the dome towers
above
the heavens, achieving and even surpassing the aspirations of the ill-fated Babelites.

Alberti wrote this famous description of the cupola soon after setting eyes on the half-built structure for the first time in 1428, following his return to Florence from exile. The wealthy Alberti clan had been banished from the city seventeen years earlier, when Leon Battista was only four, and he had subsequently been raised in Padua and Bologna. Later famous for his books on painting and architecture, in 1428 he was known for spectacular feats of physical prowess such as piercing an iron breastplate with an arrow and leaping over the shoulders of ten men in succession. Among numerous other accomplishments, he was a horse tamer and the author of treatises on both the arts of navigation and the manners of his pet dog. He invented a disk to compose ciphers (a sort of prototype of the Enigma machine) as well as an astrolabe to survey the ruins of Rome. No subject seemed to escape his attention: Greek, Latin, law, mathematics, geometry. But he took a special interest in architecture, particularly in Filippo’s dome, over the top of which, according to legend, he was able to throw an apple.

For Alberti as for everyone else in Florence, watching the dome rise above the city was the most enduring and breathtaking spectacle of the age. Alberti was probably the most interested and informed of these observers, acting as a reliable eyewitness to what later writers have doubted, namely that the cupola was raised without a wooden centering. And he makes an intriguing observation about this engineering feat, which he says “people did not believe possible.” A polygonal dome can be constructed without a wooden support network, he claims, only if “a true circular one is contained within the thickness.”