The Mechanics of Dome Building (Week 6, Blog 1)

View of the Florence Duomo towering over Florence.
Photograph by Annie Bigelow

Leone Battista Alberti wrote of Filippo Brunelleschi in his dedication of On Painting saying, “What man however hard of heart or jealous, would not praise Filippo the architect when he sees here such an enormous construction towering above the skies, vast enough to cover the entire Tuscan population with its shadow, and done without the aids of beams or elaborate wooden supports? Surely a feat of engineering, if I am not mistaken, that people did not believe possible these days and was probably equally unknown and unimaginable among the ancients.”

Taccola’s caption read: “It is built for four reasons.
First, because it turns rapidly. Second, because it
facilitates lifting as large weights are raise on high.
Third, because it runs forward and not backward.
Fourth, it does not waste time”

I was intrigued when I read this by the mechanics of exactly how the Dome was built, especially “without the aids of beams or elaborate wooden supports”. So I did some digging. Brunelleschi couldn't build centered scaffolding like one normally would, as there wasn't enough wood available to build scaffolding for the 42 meter diameter dome.

Not having a centralized scaffolding system raised many problems, including the problem of getting thousands of tons of materials up to the top of the Dome. As a solution, he designed and built a new hoist mechanism. While Brunelleschi kept notebooks with his engineering ideas, they no longer exist – meaning there are no original illustrations or designs for his hoist mechanism. Luckily one of his contemporaries and confidant, Mariano di Jacopo, known as Taccola, did document Brunelleschi’s ideas. Taccola published two works called, On Engines and On Machines. In them are illustrations of Brunelleschi’s machines that he used to build the Dome. One illustration (shown left) depicts the new hoisting mechanism the Brunelleschi developed. It features a series of wheels and counterweights and was horse powered, quiet literally. 

Bibliographical note: Toby Lester's Da Vinci's Ghost specifically Chapter 5 "The Artist-Engineer" was used as reference for information on Brunelleschi's hoist mechanism.