There were other lifts that could lift heavier loads by having horses or oxen walk in a circle, rotating a vertical shaft that was geared to turn the horizontal shaft connected to a pulley above. However, this method had a fundamental drawback: while it could lift heavier loads it could not effectively lower them down into position. Animals do not like to walk backwards, so to lower the loads once they reached their desired height it was necessary to remove the oxen’s yokes, turn them around, re-yoke them and walk them in the opposite direction. This time-consuming process significantly slowed the construction.
Some of the stones needed to build this dome weighed several tons each and needed to be precisely fit into position hundreds of feet above the ground. The human treadmill option simply could not do this work so the need to use of beasts of burden was obvious. The issue of how could these loads be raised to such vast heights and then gently lowered into place became prominent. The solution Filippo developed to solve this problem solidifies his place in history as one of mankind’s greatest inventors in my humble opinion.
Filippo must have relied on his past apprenticeship as a clock maker to invent a hoisting machine with intricate gearing and a clutch mechanism that enabled it to lift and lower great loads while the oxen continued to walk in the same direction. While the oxen rotated a vertical shaft to which they were tied, a series of cogged wheels were used that could be engaged or disengaged by a workman on the ground via the clutch mechanism. By altering which cogged wheel was employed the direction with which the hoist operated could be reversed easily.
The hoist Filippo invented was a grand and celebrated machine, about the size of a small house, sitting on the floor of the cathedral directly below the opening. It proved to be one of the most critical developments in the dome’s construction, and the reversing clutch would become one of the fundamental parts of modern engines. Giorgio Vasari, one of Filippo’s biographers wrote a century later that this machine was so ingenious that “one ox could raise what six pairs could scarcely have raised before”.
Most sources I have researched agree that Filippo’s hoisting device was decades, if not a century ahead of its time. The hoist was fast compared to previous machines, raising about fifty loads per day. It is estimated that 60 to 70 million tons of material went into the construction of this dome, and all were lifted with this amazing device.
Filippo also invented load positioning machines used on the scaffolding above to move the loads laterally to their needed place in the construction. True to form, Filippo did not document his inventions but other people did, including Leonardo Di Vinci several decades later. It is believed that some of Leonardo’s famous sketches are renderings he made trying to document mechanisms invented by Filippo Brunellschi.* In regard to the dome, one of Leonardo’s earliest assignments as a young apprentice was to help build the bronze sphere atop the lantern, crowning the dome.
* As an interesting side note, Filippo and Leonardo had remarkable similarities: both were acclaimed artists and inventors, both used secretive coded language to record their ideas, and both experienced dramatic failures when they dabbled in hydrology (the science of water movement). Filippo’s failure occurred when he concocted a plan to dam a river to flood and destroy Florence’s enemy, the nearby city-state of Lucca. It ended disastrously when Lucca hastily built a dike to protect their city from the man-made flood, then snuck across the river and breached the dam onto Florence’s encamped army. It humiliated the Florentines and greatly tarnished Filippo’s reputation.
Leonardo’s adventure in hydrology occurred sixty years later when he devised a scheme to re-route the Arno River, supposedly to improve Florence’s access to the sea, but the proposed plan would also conveniently divert the river from flowing through another enemy city-state downstream…Pisa. Without the Arno River, Pisa would probably cease to exist. It is likely that Leonardo worked closely with another illustrious Florentine, Niccolo Machiavelli, on this project. The work to divert the river was underway and going well when a freak storm destroyed much of their progress. Due to the mounting costs, the city leaders decided not to revive the project.