Still, many decades later, no one seemed to have a viable idea of how to build a dome nearly 150 feet across, especially as it would have to start 180 feet above the ground, atop the existing walls. Other questions plagued the cathedral overseers. Their building plans eschewed the flying buttresses and pointed arches of the traditional Gothic style then favored by rival northern cities like Milan, Florence’s archenemy. Yet these were the only architectural solutions known to work in such a vast structure. Could a dome weighing tens of thousands of tons stay up without them? Was there enough timber in Tuscany for the scaffolding and templates that would be needed to shape the dome’s masonry? And could a dome be built at all on the octagonal floor plan dictated by the existing walls—eight pie-shaped wedges—without collapsing inward as the masonry arced toward the apex? No one knew.

So in 1418 the worried Florentine fathers announced a contest for the ideal dome design, with a handsome prize of 200 gold florins—and a shot at eternal fame—for the winner. Leading architects of the age flocked to Florence and presented their ideas. From start to finish, the project was so charged with doubts, fears, creative secrecy, and civic pride that a lush tapestry of legend was woven around it, turning the story of the cupola into a parable of Florentine ingenuity and a central creation myth of the Italian Renaissance.

When the first histories were written, the losers came off particularly poorly. One contending architect, it was said, proposed to support the dome with an enormous pillar rising in the center of the church. Another suggested building it out of “sponge-stone” (perhaps spugna, a porous volcanic rock) to minimize its weight. Yet another, according to early legend, proposed that a mountain of dirt mixed with coins serve as scaffolding, to be cleared away free of charge by the money-grubbing citizenry after the dome was complete.

What we know for sure is that another candidate, a short, homely, and hot-tempered goldsmith named Filippo Brunelleschi, promised to build not one but two domes, one nested inside the other, without elaborate and expensive scaffolding. Yet he refused to explain how he’d achieve this, fearing that a competitor would steal his ideas. Brunelleschi’s stubbornness led to a shouting match with the overseers, who twice had him restrained and forcibly ejected from the assembly, denouncing him as “a buffoon and a babbler.”

Nonetheless, Brunelleschi’s mysterious design piqued their imagination—perhaps because they already knew this buffoon and babbler to be a genius. As a boy, during his goldsmith’s apprenticeship, he had mastered drawing and painting, wood carving, sculpture in silver and bronze, stone setting, niello, and enamel work. Later he studied optics and tinkered endlessly with wheels, gears, weights, and motion, building a number of ingenious clocks, including what may have been one of the first alarm clocks in history. Applying his theoretical and mechanical knowledge to observation of the natural world, he single-handedly worked out the rules of linear perspective. He’d just spent several years in Rome measuring and sketching the ancient monuments and noting, in cipher, their architectural secrets. Indeed, Brunelleschi’s life seemed to have been one long apprenticeship for building the dome of unequaled beauty, usefulness, honor, and power that Florence yearned for.

The next year the overseers met with Brunelleschi several times, eliciting more details of his scheme. They began to realize just how brilliant (and risky) it really was. His dome would consist of two concentric shells, an inner one visible from within the cathedral nested inside a wider, taller external dome. To counteract “hoop stress,” the outward, bulging pressure created by a large structure’s weight that could cause it to crack or collapse, he would bind the walls with tension rings of stone, iron, and wood, like hoops on a barrel. He’d build the first 46 feet in stone, he said, after which he would continue with lighter materials, either spugna or brick. He also assured the overseers that he could do without conventional, ground-based scaffolding. They welcomed the enormous savings in lumber and labor that would result, at least during work on the first 57 feet, after which everything would depend on how things went, “because in building, only practical experience will teach that which is to be followed.”

In 1420 the overseers agreed to make Filippo Brunelleschi the provveditore, or superintendent, of the cupola project. They added one significant caveat. Being hardheaded merchants and bankers who believed in competition as a way of ensuring quality control, they appointed Lorenzo Ghiberti, Brunelleschi’s fellow goldsmith, as a co-superintendent. The two men had been rivals since 1401, when they had vied for another illustrious commission, the new bronze doors for the Florentine Baptistery. Ghiberti had won. (Much later, an admiring Michelangelo would refer to a second set of Ghiberti’s doors as “the Gates of Paradise.”) By this time, Ghiberti was the most illustrious and politically connected artist in Florence. Now Brunelleschi, whose design for the cupola had been accepted outright, was forced to work side by side with his gallingly successful rival. The arrangement would lead to much plotting and skulduggery.

On this tempestuous note began the building of Il Cupolone (the Big Dome), a monumental project whose growth over the next 16 years became the city’s drama in miniature. The dome’s progress was a reference point for life in the city—events were predicted to occur and promises were to be kept “before the Dome is covered.” Its looming, rounded profile, so unlike the angular lines of the Gothic, symbolized the Florentine Republic’s freedom from tyrannous Milan, and even more so, the nascent Renaissance’s liberation from the airless constraints of the Middle Ages.

The first problem to be solved was purely technical: No known lifting mechanisms were capable of raising and maneuvering the enormously heavy materials he had to work with, including sandstone beams, so far off the ground. Here Brunelleschi the clockmaker and tinkerer outdid himself. He invented a three-speed hoist with an intricate system of gears, pulleys, screws, and driveshafts, powered by a single yoke of oxen turning a wooden tiller. It used a special rope 600 feet long and weighing over a thousand pounds—custom-made by shipwrights in Pisa—and featured a groundbreaking clutch system that could reverse direction without having to turn the oxen around. Later Brunelleschi made other innovative lifting machines, including the castello, a 65-foot-tall crane with a series of counterweights and hand screws to move loads laterally once they’d been raised to the right height. Brunelleschi’s lifts were so far ahead of their time that they weren’t rivaled until the industrial revolution, though they did fascinate generations of artists and inventors, including a certain Leonardo from the nearby Tuscan town of Vinci, whose sketchbooks tell us how they were made.

Having assembled the necessary tool kit, Brunelleschi turned his full attention to the dome itself, which he shaped with a series of stunning technical innovations. His double-shell design yielded a structure that was far lighter and loftier than a solid dome of such size would have been. He wove regular courses of herringbone brickwork, little known before his time, into the texture of the cupola, giving the entire structure additional solidity.

Throughout the years of construction Brunelleschi spent more and more time on the work site. He oversaw the production of bricks of various dimensions and attended to the supply of choice stone and marble from the quarries. He led an army of masons and stonecutters, carpenters, blacksmiths, lead beaters, barrelmakers, water carriers, and other craftsmen. When they were puzzled by some tricky construction detail, one biographer tells us, he’d shape a model out of wax or clay or carve up a turnip to illustrate what he wanted. Brunelleschi took particular care of his workers, both for their safety and to ensure that the dome progressed as rapidly as possible. He ordered that their wine be cut with water to keep them sharp on the heights (this provision was revoked under pressure by dissatisfied workers) and added parapets to the suspended platforms to prevent them from falling—or looking down from the dizzying height of the dome. According to popular legend, Brunelleschi could also be a hard taskmaster. When masons went on strike demanding better pay, we are told, he called in scabs from Lombardy, and relented only when the masons returned, hats in hand, and agreed to resume their jobs—at reduced wages.

He also had to contend with highly placed adversaries, led by the scheming Lorenzo Ghiberti. Brunelleschi was the project’s conceptual and operational leader from the start, yet he and Ghiberti received the same yearly wage of 36 florins. Brunelleschi’s biographers tell an amusing tale about how he finally outmaneuvered Ghiberti. In the summer of 1423, just before a wooden tension ring was to be laid around the dome, Brunelleschi suddenly took to his bed, complaining of severe pains in his side. When the baffled carpenters and masons asked how they were to position the enormous chestnut beams that made up the ring, he essentially delegated the task to his rival. Ghiberti had installed only some of the beams when Brunelleschi, miraculously on the mend, returned to the work site and pronounced Ghiberti’s work so incompetent that it would have to be torn out and replaced. Brunelleschi directed these repairs himself, complaining all the while to the overseers that his co-superintendent was earning a salary he didn’t deserve. Though this account may be tinged by hero worship, archival records at year’s end do name Brunelleschi the sole “inventor and director of the cupola,” and later his salary rose to a hundred florins a year, while Ghiberti continued at 36 florins.

Ghiberti didn’t give in. Around 1426 his assistant, the architect Giovanni da Prato, sent the overseers a large piece of vellum, still preserved in the National Archives of Florence, on which he’d penned a detailed criticism of Brunelleschi’s work, complete with illustrations. He claimed that Brunelleschi, through “ignorance and presumption,” had deviated from the original plans for the cupola, which was therefore “spoiled and put in danger of ruin.”

Giovanni also composed a violent personal attack on Brunelleschi in sonnet form. The poem calls Brunelleschi a “dark, deep wellspring of ignorance” and a “miserable and imbecile beast” whose plans were doomed to failure. If they ever succeeded, Giovanni rather rashly promised, he would kill himself. Brunelleschi replied with a barbed sonnet of his own, warning Giovanni to destroy his poems, “lest they sound ridiculous when all the dancing starts, in celebration of that which he now thinks impossible.”

Brunelleschi and his workmen eventually did their victory dance, though only after several more years of doubt and struggle. In 1429 cracks appeared in the east end of the cathedral nave beside the dome, forcing Brunelleschi to shore up the walls with iron tie bars. In 1434, perhaps at Ghiberti’s instigation, Brunelleschi was jailed on a technicality regarding unpaid union dues. But soon after, he was released, and the cupola continued skyward at the average rate of about one foot per month. On March 25, 1436, the Feast of the Annunciation, Pope Eugenius IV and an assembly of cardinals and bishops consecrated the finished cathedral, to the tolling of bells and cheering of proud Florentines. A decade later another illustrious group laid the cornerstone of the lantern, the decorative marble structure that Brunelleschi designed to crown his masterpiece.

Soon after, on April 15, 1446, Brunelleschi died, apparently from a sudden illness. At his funeral he lay dressed in white linen on a bier ringed by candles, staring sightlessly into the dome he had built brick by brick, as the candle smoke and the notes of the funeral dirge spiraled into the void. He was buried in the crypt of the cathedral; a memorial plaque nearby celebrated his “divine intellect.” These were high honors. Before Brunelleschi’s time, very few people, among them a saint, were allowed burial in the crypt, and architects were mostly considered humble craftsmen. With genius, leadership, and grit, Filippo Brunelleschi raised true artists to the rank of sublime creators, worthy of eternal praise in the company of the saints, an image that would dominate the Renaissance.

In fact, he paved the way for the cultural and social revolutions of the Renaissance itself, through his complex synthesis of inspiration and analysis, his bold reworking of the classical past to the needs and aspirations of the present. Once complete, Santa Maria del Fiore was decorated by artists like Donatello, Paolo Uccello, and Luca Della Robbia, making it both the birthplace and the proving ground of the Renaissance. Brunelleschi’s dome still rises from the terra-cotta sea of Florence’s roof tiles, itself terra-cotta clad yet harmoniously proportioned, like a Greek goddess in homespun. It is mountainous yet strangely buoyant, as if the white marble ridges rising to its apex are ropes holding a zeppelin to Earth. Somehow Brunelleschi captured freedom in stone, exalting the Florentine skyline ever after with an upward-yearning embodiment of the human spirit.