Brunelleschi's Dome: How a Renaissance Genius Reinvented Architecture

The construction of the dome of the Santa Maria del Fiore Cathedral was helped by the invention and construction of innovative new machines by Filippo Brunelleschi. Leon Battista Alberti, a philosopher and Brunelleschi admirer, wrote in the 1440s about the “construction of giant hoists and cranes” which allowed workers on the site to lift huge weights to lofty heights (58). The sandstone beams, for example, weighed 1,700lbs each, so Brunelleschi designed “one of the most celebrated machines of the Renaissance” (59), a hoist which could lift the beams to the height of construction. Earlier, the workers had used a treadmill-powered winch, but this was deemed inadequate. Brunelleschi designed an ox-powered alternative, which employed “one of the longest and heaviest ropes ever manufactured” (60). Importantly, the machine used reversible gears in such a way that the hoist could be raised or lowered without needing to turn the ox around, thus saving time. According to one commenter, Brunelleschi’s design was “centuries ahead of the technical understanding of the time” (62). Brunelleschi invented (or reinvented) many machines intended to help with the construction of the dome, implementing technologies such as the Lewis bolt which are now in common use. Just one of Brunelleschi’s hoists raised 50 loads a day over the course of the years-long construction project.

Similar technologies had been invented by ancient Greeks and Romans. During Brunelleschi’s time, the plans for these technologies were only just being rediscovered and translated from Greek or Latin into Italian. Just as the arts of the Renaissance were informed by the rediscovery of these ancient techniques, so was the architecture of the era. Brunelleschi, speaking no Greek or Latin, was unlikely to have had access to this wealth of information. Instead, King suggests, his innovation came from “his own experience” (65). A late 15th-century biography of Brunelleschi, attributed to his contemporary Antonio Manetti, credits Brunelleschi’s work on mechanical clocks for his engineering expertise. The spring-powered clocks which Manetti credits to Brunelleschi would not become widespread for another century, though none of these devices have survived to the modern era. The Opera del Duomo nevertheless credited Brunelleschi for his inventions and paid him 100 florins for “for his ingeniousness and labors in connection with the device newly invented by him for hoisting” (66).

Brunelleschi’s design for the dome included the implementation of a number of chains. After the construction of the ox-hoist, the first of these sandstone chains was to be installed. The complex design was made of “two concentric rings of stone laid horizontally around the octagonal circumference of the dome” (72). These two concentric rings were built into the brickwork and joined together by transverse stone beams. The sandstone was quarried in the hills around Florence. Each of the beams was 7.5 feet long and 17 inches in section with notches cut into the stone for the installation of the transverse beams. The first chain used more than 100 of these long beams, as well as many shorter beams. At each corner of the octagonal dome, the circumferential stones met at 45-degree angles and were joined together with iron clamps. The clamps were then glazed with lead to prevent rusting.

The first sandstone chain was one of four such chains. These four bands encircled the dome at intervals of 15 feet. The second chain was more complex. In 1425, Brunelleschi showed off his model for this chain, which featured radially disposed transverse beams resembling the spokes of a wheel. They were also angled rather than horizontal. The stone and iron chains are hidden from view, so their exact composition remains a mystery.

In 1424, a fifth chain made of wood was added 25 feet above the first, sandstone chain. Brunelleschi had originally planned for four such chains, all made of wood. In practice, however, he was forced to use chestnut spliced with oak clamps. He only installed one wooden chain. The wooden, stone, and metal chains helped to create the “system of invisible buttressing” (76) which supported and distributed the immense weight of the dome without the buttress which were so closely linked to Gothic architecture. Manetti alludes to hidden innovations which Brunelleschi included to protect against earthquakes and natural disasters, though these have not been reliably uncovered. Likewise, the installation of the first wooden chain may have formed part of Brunelleschi’s ongoing rivalry with Ghiberti, with Brunelleschi hoping to expose his rival’s lack of practical knowledge.

Although Ghiberti and Brunelleschi were both appointed to oversee work on the dome, Brunelleschi had “swiftly eclipsed” (78) his rival. The wooden chain gave Brunelleschi another opportunity to discredit Ghiberti. When the timber arrived in Florence, Brunelleschi took to bed with a sickness. Ghiberti was tasked with overseeing the installation of the wooden chain. Since Ghiberti was not privy to Brunelleschi’s secretive plans, however, the work ground to a halt. Suddenly, the healthy Brunelleschi returned to the site and criticized everything Ghiberti had done, demanding that the chain be rebuilt. The chain became a way for Brunelleschi to expose Ghiberti’s “incompetence to both the wardens and the people of Florence” (80). As a result, Brunelleschi’s salary was tripled while Ghiberti’s remained the same.

The story of the feigned illness resembles another elaborate trick from Manetti’s account of Brunelleschi’s life. In Manetti’s book-length story, The Tale of the Fat Carpenter, a fictionalized Brunelleschi recruits people across Florence to convince a carpenter named Manetto di Jacopo that he had metamorphosed into someone else. People around Florence spoke to Manetto as though he were Matteo, another Florentine man. King likens Brunelleschi’s elaborate practical joke to his explanation of linear perspective, in which “he showed the viewer of the painting a clever fabrication that tricked him into mistaking the artificial for the real [just as he] fashioned a unique perspective for Manetto by reordering and controlling his perceptions” (82).

A key issue in constructing the dome was ensuring that the two shells rose in tandem. Even a slight deviation in the stonework or masonry could have been disastrous. The masons on the site had “basic measuring devices” (84) such as plumb lines and levels. Brunelleschi again invented devices to aid the construction of his dome. A cord stretched from the center of the dome to the circumference, for example, could be used to determine the order and curvature of the bricks and mortar. Like many of Brunelleschi’s inventions, such a device—a trammel—is now common for bricklayers working on curved walls.

Despite the effectiveness of Brunelleschi’s inventions, he still faced criticism. In 1425, Giovanni da Prato—an ally of Ghiberti—accused Brunelleschi of betraying the intentions of the original model designed by Neri di Fioravanti, particularly in disregarding the so-called pointed fifth shape of the Fioravanti’s proposed dome. The “pointed fifth” is higher than semicircular or rounded shapes and generates less radial thrust, giving it structural advantages over domes of shallower angles. Prato accused Brunelleschi of building a rounded, rather than a pointed, dome. He claimed that Brunelleschi would “brazenly spoil and endanger the church” (88), insisting that he would not be to blame when Brunelleschi’s shortcomings were revealed. 

Prato’s claims were without basis. Instead, Prato was jealous of Brunelleschi, whose designs (and the accompanying prize money) had been selected ahead of Prato’s own submissions. Prato also continued to make his complaints about the potential lack of light in the cathedral, insisting that the lack of windows would result in a “murky and gloomy” (90) atmosphere. In this respect, the proliferation of light in cathedrals was very much a Gothic ideal. During this early part of the Renaissance, scholars debated whether a darker space might be more reflective and somber. Prato’s complaints were ignored, and Brunelleschi was given another pay raise. As such, Brunelleschi consolidated his influence over the project and pushed his rivals Prato and Ghiberti to the periphery.