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Deciphering Da Vinci’s Real Codes

Investigative Files

Joe Nickell

Skeptical Inquirer Volume 31.3, May / June 2007

The quintessential Renaissance man, with personas ranging from architect to zoologist, [1] Leonardo da Vinci was also something of a cryptographer, and much attention has been given his various “codes” [2] — both real and imagined, the latter most famously in Dan Brown’s popular mystery novel, The Da Vinci Code (2003).

Da Vinci’s ‘Codes’

Although The Da Vinci Code is fiction, Brown claimed portions were based on fact, notably that a secret society called the Priory of Sion was “a real organization” founded in 1099 and that parchments brought to light in 1975, Les Dossiers Secrets, named among its members Leonardo da Vinci (2003, 1). Alas, the parchments “were conclusively proven in the 1990s to have been part of an elaborate hoax” (Bernstein 2004, 9).

The hoax had snookered the authors of two pseudohistories, Holy Blood, Holy Grail (Baigent et al. 1996) and The Templar Revelation (Picknett and Prince 1998), on which Brown relied. The coauthors of The Templar Revelation, “researchers” Lynn Picknett and Clive Prince, had made a previous foray into nonsense (1994) with the claim that Leonardo had created the Shroud of Turin, even though the shroud appeared a century before the birth of Leonardo (1452—1519). The duo believe the image on the cloth (actually the work of a confessed forger of the mid-1350s [Nickell 1998])—was produced for two reasons. It represented both “an innovative technique” (Leonardo, they suggest, invented photography to create the image!) and “an encoded heretical belief” (he supposedly faked blood on the image as still flowing so as to indicate that Jesus did not die on the cross) (Picknett and Prince 1998, 25, 289).

For his novel, Brown borrowed from a chapter of The Templar Revelation titled “The Secret Code of Leonardo da Vinci.” There, Picknett and Prince (1998, 19—35) claim that Leonardo’s famous fresco The Last Supper contains hidden symbolism relating to the true Holy Grail. Supposedly the old French word Sangreal is explained not as san greal, “holy grail,” but as sang real, “royal blood,” revealing that Jesus married Mary Magdalene and fathered a child, thus beginning a bloodline that led to the Merovingian dynasty (a succession of kings who ruled present-day France from 481 to 751). The hoaxed parchments, Les Dossiers Secrets, provided evidence of this allegedly historically guarded secret.

Picknett and Prince claim, for instance, that St. John, depicted in The Last Supper and seated at the right of Jesus, is actually a woman—Mary Magdalene—and that the shape made by “Mary” and Jesus is “a giant, spreadeagled ‘M,’ almost as if they were literally joined at the hip but had suffered a falling out or even grown apart” (Picknett and Prince 1998, 19—21). In this and some of the artist’s other works, the authors imagine, are hidden clues to an underground religion based on the sang real secret.

By following such ridiculous sources, Brown provokes one critic to observe that his characterizations “bear little resemblance to the serious thinking in the field” of Leonardo studies and reveal “a stunning lack of careful knowledge” about his subject (Bernstein 2004, 12).


In The Da Vinci Code, the hero and heroine follow a series of cryptic clues to solve the mystery. At the beginning, some numbers are discovered scribbled on the floor beside the body of the murdered Jacques Saunier. Heroine Sophie Neveu, Saunier’s granddaughter, happens to be a “cryptographer” (actually a cryptanalyst, one who solves, rather than creates, secret writings). She recognizes the numbers as a scrambled Fibonacci sequence (a mathematical progression derived by another Leonardo, Leonardo Fibonacci [ca. 1170—ca. 1240]) and it enables her and her fellow quester, “symbologist” Robert Langdon, to unlock a safe box in a Zurich bank.

Inside they discover a cryptex, a device whose invention is attributed to Leonardo da Vinci. However, not only did he not conceive the imagined gadget but, as Brown describes it, it would not work. Supposedly it contains a scroll that can only be gained by lining up its dials correctly; smashing it open will break a phial of vinegar that will “quickly dissolve the papyrus,” so that “By the time anyone extracted the secret message,” Sophie explains, “it would be a glob of meaningless pulp” (Brown 2003, 201).

In fact, vinegar has no such effect on papyrus, which—since I am quite familiar with that writing material (Nickell 1990, 71)—I already knew instinctively; however, in honor of Leonardo, I confirmed that by a simple experiment in my lab. There was no appreciable affect even after weeks.

‘Code’ Script

In Brown’s tale, the rosewood box containing the cryptex also yields an engraved riddle, itself rendered in a baffling script that is finally recognized as mirror writing. That backward form was employed by Leonardo throughout his celebrated notebooks (see figure 1). People have long puzzled over his reason for so writing, one popular hypothesis being “to keep people from peering over his shoulder and stealing his ideas,” notes Brown (2003, 301). Indeed some have even called it a code, a possibility supposedly made more credible by Leonardo’s having “often employed codes and ciphers to disguise his ideas further” (White 2000, 131). Specifically, it has been pointed out “that in very specific circumstances Leonardo would invent code writing (for example, in the so-called Ligny memorandum of about 1499, recording the artist’s journey to Rome with the count of Ligny).” As well, he “created playful rebuses and cryptic pictographs” (Bambach 2003, 33).

For a time, when he feared two German assistants were spying on him, his writings reflect anxiety and “are written not only in his usual mirror-writing but heavily encoded, with imagery more at home in alchemical texts than his notebooks” (White 2000, 250). Iris Noble (1965, 139) has suggested that his treatise De Figura Umana (On the Human Figure) was so “dangerous” in exploring anatomy even through dissections of corpses that “He wrote it in mirror language because he knew well that times would have to change before that book could be printed for all to see.”

But is that really the case? Leonardo definitely intended that book—along with many other treatises in progress—for publication. And as one writer observes, “the labor of writing backward would surely have been out of all proportion to the secrecy value, since the script could be read by anyone with a mirror” (Linscott 1957, xiii). Besides, Leonardo copied much extraneous and innocuous material into his notebooks in backward script, including portions of a Latin grammar, various quotations, even jokes (Linscott 1957, xiii).

Others have suggested that the mirror-writings could be due to dyslexia (Priwer and Phillips 2005, 210); however, the fluency of their exposition and elegance of reasoning as well as their quantity and even the stylish calligraphy of some early notes are scarcely consistent with such a diagnosis. Moreover, Leonardo was apparently also to some extent ambidextrous and could employ conventional, left-to-right script when necessary, as in writing letters. That has been disputed, but now the scholarly consensus is that occasionally he did do so (Bambach 2003, 33, 44).

Most knowledgeable authorities now attribute the backward penmanship to Leonardo’s having been left-handed. The earliest testimony of that fact comes from his close friend and collaborator, Fra Luca Pacioli (ca. 1445—ca. 1514), who stated that Leonardo “wrote in reverse, [his script] is left-handed and could not be read except with a mirror or by holding the back of the sheet against the light. As I understand, and can say, this is the practice of our Leonardo da Vinci, lantern of painting, who is left-handed” (qtd. in Bambach 2003, 32).

The right-to-left mode would have been an advantage to a left-handed writer, since otherwise the hand would trail over and smear the wet ink (unless its position or that of the paper was radically altered). Having chosen to write in reverse fashion, Leonardo would no doubt have enjoyed its fringe benefits: its difficulty of being deciphered by casual readers, and the attention he gained from the novelty of performing such a trick.

Another Possibility?

Over the years (by 1983), I had begun to wonder if Leonardo might have received another benefit from his mirror-writing. I was intrigued that there is an important art form that actually utilizes mirror-writing and drawing; indeed, it is one that Leonardo would have been very familiar with. In fact, while there is no clear evidence that he practiced that art himself, he is known to have made the preliminary drawings—for another such practicing artist to copy—to illustrate his friend Pacioli’s treatise De Divina Proportione (On Divine Proportion) (White 2000, 153).

The art I am referring to is that of printmaking—either by engraving or woodcut. To make prints, the respective copper plate or wood block is carved (incised for the former, cut in relief for the latter) in reverse (Nickell 1992). Thus, the plate is a mirror image of the print it makes.

Since Leonardo intended his works to be published, might not he have taken advantage of his left-handed ability to write in reverse in order to assist future mirror-writing artisans in copying his text? Although many books of his time were set in moveable type (following its introduction ca. 1450 and its first use in Italy in 1465 [Nickell 1990, 127]), woodcuts and engravings were still also common. Engraved copper plates could have seemed an ideal method of reproducing Leonardo’s pages with their interwoven illustrations and text.

One immediately thinks of arguments for and against this hypothesis, but serious investigators learn to avoid drawing firm conclusions too quickly. (I frequently encounter people who are such bright, quick thinkers that they finish my sentences for me—often incorrectly. Over time, I have been trying to teach myself to think more slowly, that is, more carefully.) I approached the puzzle of Leonardo’s “code” writing as if (and I have had some experience in this regard [3]) I were solving a cryptogram.

In the notebooks, not only is Leonardo’s text reversed but apparently drawings are as well, some diagrams being so indicated by the fact that their sequential letters—a, b, c, etc.—run from right to left (see, e.g., illus. in Bambach 2003, 598). Moreover, Carmen C. Bambach (2003, 51), curator of Drawings and Prints at the Metropolitan Museum of Art, observes that the evidence indicates Leonardo was a “‘natural’ left-hander” and that

He had an uncanny mental ability to reverse, as if in a mirror, both writing and images fluently; not all left-handed artists have this ability. Preliminary drawings show that he seems often to have tried out mirror images of a similar compositional idea, perhaps to stir up his creative juices in designing the figural arrangements of his pictures. This unusual, very prominent feature of his creative process has been little discussed by scholars.

Although Leonardo put little of his material in final order, he did keep most of his observations to a single page, noting carefully if they were continued (Richter 1883, xv). Of course, not all of his scattered pages were intended for publication; some were simply sketches and drawings per se, while others bore mundane notations and reminders. Yet some were like a set of studies of the human skull, begun in 1489, that “reveal a neat, treatiselike disposition of image and text on the page (as well as the technique of exquisitely fine parallel hatching that is typical of engravings from this period)” (Bambach 2003, 15). Were Leonardo’s pages of this type actual models for a future engraver? Might he have at least been aware of his mirror-writing’s utility in this regard?

. . . Or Not?

Clearly there is a similarity between, on the one hand, certain of Leonardo’s pages that were apparently intended for publication, and, on the other, the engraved copper plate that could have reproduced them as conventional (non-reversed) pages to be read by others. Even if it was just a coincidence, Leonardo must have noticed and appreciated the fact of the similarity.

As I studied the matter, I realized the need to find among Leonardo’s figures—that is, among those that were seemingly intended for publication—one or more that were unmistakably mirror-imaged.

What I found, however, placed me in the unfortunate position of having to debunk, or at least urge skepticism of, my own hypothesis. It came in the form of a drawing of 1490 that “may have been intended to illustrate a treatise on anatomy” (Bambach 2003, 409). Labeled the “tree of veins” and illustrating internal organs in a pioneering cutaway view of a male figure, it places the heart on the figure’s left, that is, in non-reversed fashion. The same is true of a 1508 anatomical drawing of a female, and still others (White 2000, 284; Leonardo 1956, 369, 371, 377).

This seems clear evidence against my otherwise very intriguing hypothesis. Of course, there may be something in the idea after all. At least, it might inspire others to take a fresh look at Leonardo’s great gifts to us. Perhaps, avoiding the silliness of the pseudohistorians who have abused and slandered him, they will decode some further secrets of his genius.


I appreciate the assistance of artist/art scholar Glenn Taylor, who made helpful criticisms of my Leonardo mirror-writing-for-engraving hypothesis, and CFI Libraries Director Timothy Binga, for research assistance.


  1. At least, Leonardo did architectural drawings (and was an occasional architectural consultant), and he studied animals, sketching their form and movements, visiting slaughterhouses to observe still-beating hearts, studying the flights of birds, etc. (Phillips and Priwer 2006, 103—116, 190—191, 126—127).
  2. Although the term code is often used very loosely, cryptanalysts distinguish between a code (where arbitrary symbols, words, etc., stand for certain whole concepts, such as words, phrases, or the like) and a cipher (in which letters of the “plaintext” are transformed—by substitution or transposition—to conceal its meaning).
  3. See the illustrated short treatise on “Secret Writing” in my book, Pen, Ink, & Evidence (Nickell 1990, 176—178); see also my decipherment of the Oak Island mystery’s cipher-stone text and symbol-ridden allegory (Nickell 2001, 219—234).


Joe Nickell

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Joe Nickell, Ph.D., is Senior Research Fellow of the Committee for Skeptical Inquiry (CSI) and "Investigative Files" Columnist for Skeptical Inquirer. A former stage magician, private investigator, and teacher, he is author of numerous books, including Inquest on the Shroud of Turin (1998), Pen, Ink and Evidence (2003), Unsolved History (2005) and Adventures in Paranormal Investigation (2007). He has appeared in many television documentaries and has been profiled in The New Yorker and on NBC's Today Show. His personal website is at