By Stas Margaronis
On August 19, 1418, Filippo Brunelleschi was awarded the contract to build the dome that would enclose the Florence cathedral Santa Maria de Fiore. Brunelleschi would dedicate the next 28 years to solving the puzzles of the dome’s construction. In the process, he did nothing less than reinvent the field of architecture according to King. Denounced at first as a madman, Brunelleschi was celebrated upon completion of the dome’s construction as a genius.
Brunelleschi was inspired by the construction feats of ancient civilizations including the domed Pantheon at Rome, the largest dome of its time not supported by beams or other means of supports. Brunelleschi studied its construction and was inspired to replicate the concept for the dome at Santa Maria de Fiore in Florence. The construction of the cathedral begun in 1296 [1] but its completion would have to wait until 1418 for someone with the expertise to build the 143 foot in diameter dome without vaulting which remains the largest dome in the world.
One of the most important engineering achievements was Brunelleschi’s design of a system of gears so that oxen could raise and lower building materials hundreds of feet into the air. Brunelleschi’s “ox-hoist was remarkable for both its sheer size and power and for the complexity of its design, especially its reversable gear, an important innovation for which there is no known precedent in the history of engineering… It consisted of a wooden frame, 15 feet in height, to which were attached a number of horizontal and vertical shafts or spindles that rotated each other by means of cogged wheels of varying sizes. The machine was set in motion by either one or two oxen yoked to a tiller that turned the vertical shaft.” [2]
With no comparable technology available at the time, one of the great mysteries is how Brunelleschi discovered this technology and expertise: “The exact inspiration for this remarkable machine remains as mysterious as that behind Filippo’s other inventions. The specialist theoretical knowledge needed for constructing such a hoist was largely unavailable in 1420, though soon afterwards a number of manuscripts on Greek mechanics and mathematics began arriving in Florence, putting architects and inventors of the Renaissance in possession of engineering techniques far beyond those available in the Middle Ages.” [3]
Ancient Greek manuscripts began to arrive in Florence primarily from the Byzantine capital of Constantinople. This flow of manuscripts was to lead to a rebirth or ‘Renaissance’ of learning from ideas emanating from Antiquity In 1423, two years after Brunelleschi finished building his hoist, a Sicilian named Giovanni Aurispa returned from Constantinople with two hundred and thirty-eight manuscripts written in Greek that included a complete copy of works of the geometer Proclus of Alexandria, a treatise on ancient lifting devices, the Mathematical Collection of Pappus of Alexandria. This “latter work, from the fourth century A.D., describes the windlass, the compound pulley, the worm and wheel, the screw and the gear train—all essential features for hoists and cranes.”[4] So many manuscripts on Greek mathematics and engineering emerged that there was a Renaissance of mathematics in Italy along with that of art and architecture.” [5]
All of these discoveries came too late to help Brunelleschi with his ox-hoist.
Other technological achievements that were incorporated into the Santa Maria de Fiore dome were:
- A method “had to be found of guiding and controlling this gradual inclination (of the bricks within the dome) a related difficulty was calculating the radial dispositions not only of the bricks, but also of the transverse sandstone beams of the second and third stone chains: all of this masonry all had to tilt inward and to radiate from the vertical center of the dome.” Traditional tools such as plum lines would not do the job.[6] King believes that Brunelleschi solved the problem of creating a guide for the bricklaying by running a cord “outward from the center of the dome to the inside etches of the masonry. This cord, which could be swept three hundred and sixty degrees around the cupola, would have risen and progressively shorten as more courses of bricks were added…” [7]
- Brunelleschi paid close attention to the safety of his workers and the construction site. As a result, only one worker died during the years of construction. These improvements included: a platform that acted as a safety net, a requirement that workers wore safety harnesses and a restriction on wine consumption on the job.[8]
- Another innovation was the herringbone pattern of bricklaying: “The incomplete courses of bricks were therefore held in place not by an internal support (as in the case of a wooden centering) but 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 elaborate centering, is therefore essential to the dome’s structure.” [9]
[1] Ross King, Brunelleschi’s Dome, page 5
[2] Ibid, p.60
[3] Ibid, p.63
[4] Ibid, p.63
[5] Ibid, p.63
[6] Ibid, p.84
[7] Ibid, p.85
[8] Ibid, p.95
[9] Ibid, p.98