The Italian Renaissance polymath Leonardo da Vinci (1452-1519) is justly celebrated as one of the most brilliant minds in all of human history. His unparalleled genius spanned an incredible range of fields, from his legendary paintings like the Mona Lisa and The Last Supper, to his groundbreaking anatomical studies, to his visionary designs for flying machines, tanks, and ideal cities.
Recently, scholars have debated another potential achievement to add to Leonardo‘s towering list: inventor of the first mechanical computer. A circa 1493 sketch found in a lost manuscript shows an arrangement of gears and pinions that tantalizingly resembles a 13-digit calculating mechanism. Could this be evidence that the original "Renaissance man" also pioneered the first "computing machine"?
Discovery of the Codex Madrid
The story begins in the National Library of Spain in Madrid in 1965. An American professor, Dr. Julius Piccus, was searching through library cabinets for unrelated research on medieval Spanish literature. Amidst the archive, he stumbled upon two unknown collections of Leonardo‘s notebooks, which came to be known as Madrid Codices I and II.
These remarkable manuscripts contained hundreds of pages of Leonardo‘s notes, sketches, and diagrams on a wide variety of scientific and technical subjects. Until this discovery, the Madrid Codices had been lost since the 16th century, misfiled and mislabeled in the library‘s collection. Their contents provided an invaluable window into Leonardo‘s insatiable curiosity and inventive mind.
Folio 36v: A Calculating Device?
One illustration in particular jumped out at modern scholars. On folio 36 verso of Madrid Codex I was a diagram of a sequence of 13 interlocking gears. Alongside the sketch, Leonardo had written:
"This manner is similar to that of the levers, although different, because, being this made of gears with their pinions, it can move continuously, while the levers cannot."
To Dr. Roberto Guatelli, an Italian expert who had been building models of Leonardo‘s machines for IBM since the 1930s, this looked remarkably like a schematic for an early analog computer. Each of the 13 gears was labeled with a "1" or a "10," suggesting they represented decimal places, while the accompanying text described a device that could produce continuous rotary motion.
In 1968, Guatelli created a full-scale replica of the mechanism and put it on public display, with placards boldly proclaiming it as a "Leonardo da Vinci Device for Calculation" and an "early version of today‘s complicated calculator." The machine used a 10:1 gear ratio to increment decimal places, such that a full revolution of the input shaft would turn the ones place gear 1/10 of a rotation, carrying over to the tens place, and so on for 13 digits.
This raised the explosive possibility that Leonardo had designed the first working mechanical calculator, over 150 years before the inventions of Wilhelm Schickard and Blaise Pascal in the 1600s. Had one of the greatest geniuses of all time also been the first to envision and describe a "computer"?
Academic Debate and the MIT Symposium
Almost immediately, the sensational claim drew skepticism and criticism from the scholarly community. At a public symposium at MIT in 1969, Leonardo experts presented numerous arguments against the calculator theory:
- The sketch did not show any means of inputting numbers, such as dials or adjustable pins
- There was no carry mechanism or way to read the result, which are essential parts of a practical calculator
- The gears would have generated far too much friction to be workable with Renaissance-era manufacturing precision
- No other drawings or notes referred to the device as a calculator, only as a study of ratios and continuous motion
In a vote at the end of the symposium, the participants were evenly split on the question. While some continued to believe it was an early design for a computer, the majority view emerged that Leonardo meant the drawing only as a theoretical demonstration of the properties of gears, not a practical machine.
Faced with this academic pushback, IBM voluntarily withdrew the model from public display. But the controversy had shined a spotlight on a neglected area of the history of computing. Even if Leonardo‘s particular device was not a true calculator, investigating it raised fascinating questions about when and how the core concepts of mechanical computation first began to emerge.
The Evolution of Mechanical Calculation
Looking at folio 36v with modern eyes, it‘s clear that Leonardo had hit upon one of the key ideas that would make mechanical calculators possible: using meshed gears to control numeric ratios. The way the device was drawn, each gear represented a decimal digit, and a full revolution of the first gear would increment the second by 1/10 of a turn, carrying over any excess to the next place value.
This is precisely the mathematical property that allows a machine to perform addition through the accumulation of rotations. It‘s the same principle that would later be used in the Pascaline, Leibniz wheel, Arithmometer, and other early mechanical computers. If we imagine connecting the gears to some form of input sliders or keys and output dials, it‘s tantalizingly close to a working decimal calculator.
However, it‘s equally clear that Leonardo‘s sketch was missing several crucial components that would be necessary for a practical machine. There was no way to set the operands (the numbers to be added), no carry mechanism between digits, no selvage or clearing to end a calculation. And the scholarly consensus is that Leonardo never pursued those additional elements because he was not actually trying to build a complete device.
Instead, Leonardo seems to have been exploring a more abstract idea, using gears to precisely generate and control numeric ratios. This was likely inspired by the development of geared astronomical clocks in the 14th century, which used stacked wheels to represent cycles of hours, days, months, years, etc. It was a novel intellectual leap to imagine using similar mechanisms to represent arbitrary decimal numbers.
From this perspective, folio 36v is best understood as a "thought experiment", a tinkering with the possibilities of an emerging technology. It‘s unlikely that Leonardo built even a prototype of the device, let alone a complete working model. But his Madrid drawing represents an important milestone in the prehistory of computing, a glimmer of the mechanical calculation techniques that would flourish centuries later.
A Glimpse at a "da Vinci Computer"?
It‘s also fascinating to consider how the discovery of the Madrid Codices in 1965, right at the dawn of the electronic computer age, influenced how Leonardo‘s "calculator" was interpreted and understood. If the same manuscript had been found 100 or 200 years earlier, it may not have jumped out as a computing device at all.
But in the mid-20th century, as IBM and other companies were racing to develop electronic computers, society was primed to see Leonardo‘s gears as an early conception of calculational hardware. The famous Gear Sketch looked remarkably similar to the switching circuits and logic gates that were powering the first generation of digital computers. It‘s no wonder it captured the imagination of the public and scholars alike.
So what might a completed "da Vinci computer" actually have looked like? Based on the Madrid sketch, we can envision rows of decimal gears mounted in a large wooden frame, with brass input sliders to set the digits of the addends. Levers and pins could engage and disengage the gear trains to perform carries between places.
An output dial at the end of the register could display the result, while a crank handle would be turned to power the addition cycles. With some clever engineering, it may even have been possible to chain multiple operations together, presaging the "program steps" of 19th-century devices like the Analytical Engine.
Of course, Leonardo never described any such details, so this device must remain firmly in the realm of historical speculation and fantasy. If the calculating machine interpretation is correct, then the gear trains on folio 36v would have been only the kernel of an idea, not a complete design or invention.
But it‘s thrilling to imagine a world in which Leonardo‘s genius had been combined with the advanced manufacturing capabilities and materials of later centuries. If a calculating machine had been a real priority, instead of just a passing thought experiment, there‘s little doubt Leonardo would have had the brilliance to design it. A true "da Vinci computer" may have jumpstarted the development of mechanical calculation by a century or more.
Renaissance Art Meets Digital Design
Leonardo‘s Madrid "calculator" also highlights another fascinating connection between his innovations and modern computing: the intersection of art and engineering. Leonardo is celebrated not only for his technical creativity, but for his iconic drawings and fusing of art and science. His anatomical sketches, maps, flying machines, and ideal city plans are all gorgeously illustrated with detail, shading, and multiple perspectives.
In the same way, today‘s digital artists and designers rely on computer software that merges mathematical precision with creative expression. Leonardo‘s draft of an adding machine built from gears is mirrored by modern CAD schematics and 3D graphics rendered through billions of computations. His sketchbooks gave rise to the idea of the artist-engineer, which programmers and innovators from Steve Jobs to John Maeda have aimed to emulate.
It‘s captivating to imagine how Leonardo might have employed digital tools in his own art and research, from crafting perfectly proportioned composition to digitally mapping the "Vitruvian Man." When Leonardo wrote that "man is a model of the world," he was perhaps anticipating how computers would one day be used to build virtual models and simulations of almost every aspect of reality.
And with his unique genius for both aesthetic grace and mechanical invention, it‘s hard not to wonder what wonders Leonardo could have created with a full-fledged arithmetic engine at his disposal. His tragically unrealized "Ideal City" could have been plotted and constructed with digital precision. He could have expanded his fascination with calculation to cover algebra, geometry, and even the foundations of calculus.
Legacy of a Timeless Mind
In the end, of course, these dreams of a "da Vinci computer" must remain alternate history. The Renaissance was constrained by the manufacturing and material limitations of its time – just like our visions of the future are constrained by the technological boundaries of the present. Leonardo‘s bold ideas could not find full expression with the tools of the 15th century, no matter how brilliant the mind behind them.
But this is also why his Madrid "calculator" sketch remains so compelling, even if it was not a complete computer design. It gave us a glimpse of a genius leaping beyond the assumptions and conventions of his own era, imagining mechanisms that could offload a sliver of mankind‘s mental effort to tools of brass and wood.
At a time when even the most educated elites used only pen and paper to tackle arithmetic, Leonardo dared to conceive of a machine that could add, carry, and display numbers by turning a hand crank. And in doing so, he captured the core insight that would ignite a revolution in human civilization centuries later: That computation is ultimately a physical process that can be embodied and automated in machinery.
So while Leonardo‘s "calculator" may not have been a real computer, it stands as an astonishing feat of prescient imagination and creativity. In that fanciful arrangement of shafts and gears, we can trace the origins of a new way of seeing the world, in which the precision of mathematics could be fused with the power of industry to create thinking machines.
Somewhere in the scratched lines and scribbled notes of folio 36 verso, a Renaissance artist-scientist peered across the centuries and dreamt of the first computer. And even if it remained only a dream, the legacy of that vision continues to unfold in the electronic wonders and digital renaissance of today.
