You are the illegitimate son of a notary and a peasant woman. Your father never married your mother. You live with your grandparents and then your father, who has now married someone else. You cannot inherit. You cannot become a notary like your father. The legitimate professions are closed to you by the accident of your birth.
What you can do is draw. You have always been able to draw — since you could hold a stick. Your father, perhaps feeling some obligation, arranges an apprenticeship with Andrea del Verrocchio, one of Florence's leading artists. The workshop produces paintings, sculptures, bronze castings, goldsmithing, theatrical design, engineering work. It is the Renaissance equivalent of a technology company and a fine arts school combined.
Verrocchio works you hard. You learn to grind pigments, prepare canvases, assist with background details in the master's paintings. You are good — exceptionally good — almost immediately. Verrocchio notices. He gives you more responsibility.
You could focus on becoming the best painter in the workshop — specialize, develop mastery in one area, build a reputation. Or you could do what your curiosity pulls you toward: learn everything, investigate everything, follow every question wherever it leads.
Leonardo followed everything. His notebooks — 7,000 pages, written in mirror-script from right to left, possibly to prevent copying — contain designs for flying machines, studies of water flow, anatomical drawings from 30+ human dissections, botanical illustrations, optical experiments, musical instrument designs, military engineering, and thousands of observations about the natural world. He argued that painting required understanding all other disciplines — you could not paint water without understanding how water moved, could not paint a human figure without understanding how muscles worked under skin. This philosophy produced the greatest drawings in history and the fewest finished paintings of any major Renaissance master.
You are 30 and have been in Florence for sixteen years. You have established a reputation — you are considered one of the finest painters of your generation. But Florence already has Botticelli, Ghirlandaio, Perugino. The Medici court is full of artists.
You have decided to approach Ludovico Sforza, the Duke of Milan, for a position at his court. Milan is less saturated with artistic talent. More importantly: Ludovico needs engineers. He needs someone who can design weapons, fortifications, canals, and siege equipment for his ambitions in northern Italy.
You write him a letter. The letter lists ten skills. Nine of them are military engineering — bridges, siege weapons, armored vehicles, cannons, ships. The tenth, almost as an afterthought, is this: "In times of peace I believe I can give perfect satisfaction and to the equal of any other in architecture and the composition of buildings public and private; and in guiding water from one place to another. I can carry out sculpture in marble, bronze, or clay, and also I can do in painting whatever may be done, as well as any other, be he who he may."
You are offering yourself primarily as a military engineer. You are a painter hiding behind weapons.
Leonardo sent the letter and moved to Milan. He spent 17 years at the Sforza court — the most productive period of his life. He painted The Virgin of the Rocks, Lady with an Ermine, and The Last Supper. He designed a massive equestrian statue of Francesco Sforza (the bronze was never cast — the metal was used for cannons when the French invaded). He filled notebooks with engineering designs, musical instruments, theatrical machinery. He dissected bodies in the hospital at night and painted by day. The military engineering he promised Ludovico was partly real, partly speculative — his designs were imaginative but often impractical for actual 15th-century production. Ludovico got his court entertainment. Leonardo got seventeen years of resources and freedom.
Learning never exhausts the mind.
Before you left for Milan, the monks of San Donato a Scopeto commissioned you to paint an Adoration of the Magi — a large altarpiece showing the three wise men presenting gifts to the infant Jesus. They have paid you in advance, including land rights, and they need the painting within 24 months.
You began the work. The underdrawing is extraordinary — dozens of figures in complex perspectival arrangement, horses rearing, old men leaning forward, young men gazing upward. The composition is the most sophisticated anyone in Florence has attempted. You made a beautiful, intricate architectural setting in perspective. You have been working on the preparation for months.
You have not added a single layer of paint to the final surface.
Now you are leaving for Milan. The monks will never receive their altarpiece. Filippino Lippi will be commissioned to paint a different version 15 years later. Your unfinished panel will sit in a storeroom, unpainted, for the rest of your life — one of the most studied "unfinished" works in art history.
Leonardo left for Milan and never finished the Adoration of the Magi. He left behind at least six other unfinished commissions during his career, including the Sforza horse statue, the Battle of Anghiari (which he painted with an experimental technique that failed and began to deteriorate while he was still working on it), and Saint Jerome in the Wilderness. The pattern — begin brilliantly, lose interest before completion, move to the next question — is the defining feature of his career. Scholars still debate whether this was a flaw or a method: the sketches and underpaintings often contain more innovation than the finished works of his contemporaries.
Your notebooks contain designs for a flying machine — an ornithopter, a device with wings that beat like a bird's, powered by a person lying face-down and working pedals with their legs. You have studied birds obsessively. You have written a book, the Codex on the Flight of Birds, analyzing how wings generate lift, how a bird adjusts its weight to bank and turn, how feathers respond to wind.
You believe the machine can work. You have been refining the design for twenty years. The Fiesole hill near Florence, you have written in a note, "will give fame to the nest in which it was born." Someone will test it there.
But the machine has never been built. You do not have the resources to build it yourself. The patrons who fund your painting do not fund mechanical experiments. You would need wood, fabric, rope, metalwork, and a test pilot willing to potentially fall from a height.
You could divert income from painting commissions to fund the construction. You could find a patron specifically for the project. Or you could leave the design in the notebooks and keep developing it in theory.
Leonardo never built a working flying machine. His ornithopter designs, modern engineers have analyzed, would not have flown — the human body cannot generate enough power to sustain wing-driven flight. His glider designs, however, are more plausible, and his understanding of aerodynamics anticipated principles that wouldn't be formally described until the 19th century. A reconstruction of his designs was test-flown in 2002 and achieved brief, limited flight. The notebooks preserve 500 years of ideas that were ahead of their time — but they are drawings, not machines. Whether Leonardo knew the ornithopter wouldn't work and kept developing it anyway, or genuinely believed it would fly, is one of the unresolved questions of his biography.
Francesco del Giocondo, a Florentine merchant, has commissioned you to paint a portrait of his wife, Lisa. It is a routine commission — portrait of a merchant's wife, payment on delivery. You begin the work.
But something about this portrait is different from the beginning. You are experimenting with sfumato — a technique of layering glazes so thin that edges dissolve rather than being drawn — and the effect on the face is unlike anything you have achieved before. The smile is ambiguous. The landscape behind her is not a real landscape but a composite of everything you have observed about geology, water, atmosphere, and light. You keep working on it.
Four years pass. Francesco del Giocondo has not received his painting. You are in Milan. You are in Rome. You still have the painting. You are still working on it.
You will never deliver it. You will carry it with you for the rest of your life, still touching it in the final years. King Francis I of France will buy it from your estate after your death.
Leonardo kept the Mona Lisa. He carried it with him from Florence to Milan to Rome to France, where he lived the last three years of his life under the patronage of King Francis I. He was still making tiny adjustments to it, according to some accounts, in the final months before his death. Francis I bought it from his estate for 4,000 gold écus. It hung in the palace at Fontainebleau, then Versailles, then was moved to the Louvre during the Revolution. Napoleon Bonaparte briefly took it to hang in his bedroom. The Louvre acquired it permanently and has held it since 1797. It is currently the most visited artwork in the world. Francesco del Giocondo's wife never saw the finished version.
You have now dissected more than thirty human bodies. You have done this in hospital morgues, working at night by candlelight, in the cold, in conditions that made most people unable to function. The purpose was initially practical: to understand the human figure well enough to paint it accurately. But it has become something else.
Your anatomical notebooks contain the most accurate drawings of human internal anatomy produced before the age of printing. You have drawn the heart, the lungs, the brain, the skeleton, the muscles in layers, cross-sections of the embryo in the womb. You have identified the four chambers of the heart. You have described the function of the aortic valve in terms that would not be formally recognized by medicine for another 400 years.
A colleague suggests you should publish this work — compile it into a book of anatomy. It would be the most accurate medical reference in existence. You have all the illustrations. You have the knowledge. You need only to write the text and organize the plates.
You begin. You make notes toward a prefatory text. You keep making more dissections, which produce more drawings, which require more organization. The book grows. It is never finished.
Leonardo never published the anatomical notebooks. He kept adding to them. When he died, they passed to his assistant Francesco Melzi, who preserved them but also never published them. After Melzi died, the notebooks were dispersed, lost, sold in pieces, scattered across Europe. They were not reassembled and studied as a unified body of work until the 19th century. Andreas Vesalius published his landmark anatomy book De Humani Corporis Fabrica in 1543 — 24 years after Leonardo's death — without access to Leonardo's work. If Leonardo had published his anatomical drawings in 1510, Vesalius's book might not have been necessary. Medical history might have been different. The notebooks stayed in the drawer.
Cesare Borgia — illegitimate son of Pope Alexander VI, the most feared man in Italy, a man who poisoned rivals and murdered political opponents as a matter of routine — has hired you as his military engineer and architect. You will travel with his army as he conquers central Italy.
You have taken the position. You are mapping towns, designing fortifications, inspecting drainage systems. You are producing the most accurate maps of central Italy that have ever been made. You are also working for a man who is committing atrocities in the towns you are mapping.
In your notebooks from this period, you record everything you see — military fortifications, water channels, town layouts — without comment on the violence happening around you. Borgia's soldiers are massacring populations in some of the towns you visit. You make engineering notes.
Your closest friend from this period is Niccolò Machiavelli, who is also traveling with Borgia's court as a Florentine diplomatic observer. Machiavelli is studying Borgia for the book he will eventually call The Prince. You are drawing maps.
Leonardo stayed with Borgia for nearly a year — until Borgia's political position collapsed in 1503. His notebooks from this period contain no recorded moral commentary on what he witnessed. Historians have debated this silence ever since. Some argue that Leonardo, as an artist dependent on powerful patrons, had no realistic alternative. Others argue his silence is simply consistent with his general practice of observing the world without moral judgment in the notebooks, which were private working documents rather than moral diaries. What the period produced: the most detailed maps of central Italy of the era, and friendship with Machiavelli, who may have used Leonardo as a partial model for the rational, amoral advisor described in The Prince.
King Francis I of France has given you a house — the Château du Clos Lucé, a short walk from his palace at Amboise. He visits you often. He calls you his "dear friend." He pays you a substantial annual salary with no specific deliverables. You are, for the first time in your life, free to do exactly what you want with no obligations to complete anything.
You are 67. Your right hand has been partially paralyzed — some historians believe by a stroke — and you can no longer paint with it. You have taken to drawing with your left hand. You fill notebooks with water studies — turbulent water, water flowing past obstacles, water from above and below. You write that you have understood something about how water moves that no one has understood before.
You have 7,000 pages of notebooks. Thousands of drawings. Fewer than 20 finished paintings. Dozens of unfinished projects. The anatomical book never published. The flying machines never built. The great bronze horse never cast. The Battle of Anghiari that started and failed.
Francis asks what you regret.
According to Vasari, who interviewed people who knew Leonardo, he said on his deathbed that he had offended God and humanity by not working at his art as he should have. This is often read as an expression of regret about the unfinished work. But Leonardo's notebooks tell a different story: a man who believed that understanding something was more valuable than producing an object, that the process of investigation was itself the product. He wrote: "As a well-spent day brings happy sleep, so a life well spent brings happy death." He died on May 2, 1519, reportedly in the arms of Francis I. His notebooks passed to Melzi, were eventually dispersed, and most were not fully studied until the 20th century — 400 years after his death. When engineers finally read them carefully, they found machines that wouldn't be independently invented for centuries. The questions in the notebooks were not wrong. They were simply early.