Giambattista della Porta: The Professor of Secrets

The palazzo at Via Toledo 368 in Naples still stands. Guests can book a bed in its frescoed rooms today. Most do not know whose house this was, or what was written here that could have changed the course of European history. In 1558, the man who lived in this palazzo published a recipe. It was a simple one: a fat base mixed with certain plants, rubbed into warmed skin. The recipe proved that women accused of flying to the Witches’ Sabbath were not consorting with demons. They were unconscious on the floor, hallucinating. If anyone in power had listened, it might have slowed the machine that burned tens of thousands of people across Europe over the next two centuries.

Nobody listened. The Church made him cut the recipe from his book. A French jurist wanted him burned at the stake for publishing it. The recipe vanished from the 1589 edition of his masterwork and stayed buried for four hundred years, until a German professor rubbed the ointment on his own skin in 1960 and confirmed that it worked.

His name was Giambattista della Porta. They called him the Professor of Secrets.

What “Secrets” Meant

The word needs explaining first, because it has shifted since the sixteenth century. When della Porta and his contemporaries used the word secreti, they did not mean information someone was hiding from you. The Latin secretum comes from secernere, “to set apart.” A secret was something nature itself had set apart from ordinary perception: a hidden property of a plant, a mineral, a chemical reaction. Magnetism was a secret. The power of belladonna to dilate the pupils was a secret. The way henbane could send a person into visions was a secret.

These properties were real and observable, but they could not be explained by the standard Aristotelian framework of hot, cold, wet, and dry. They were “occult” in the original sense of the word: hidden. The job of a natural philosopher, as della Porta understood it, was to hunt these secrets down through experiment and observation, not through reading Aristotle.

By the 1580s, Tommaso Garzoni cataloged over five hundred professions in his La piazza universale and identified a distinct professional class: the professori di secreti, the professors of secrets. These were searchers after things “whose reasons are not so clear that they might be known by everyone, but by their very nature manifested only to a few.” They were not university professors. They were not charlatans. They occupied a space between the scholarly world and the marketplace, and they claimed authority through experience rather than credentials.

Della Porta was the most famous of them. He was not the first.

Before della Porta: Ruscelli’s Three Trials

In the 1540s, a humanist from Viterbo named Girolamo Ruscelli founded an academy in Naples that he called the Accademia Segreta. Its twenty-seven members, including a prince, pooled an annual budget of 7,800 scudi and set about testing recipes for medicines, cosmetics, dyes, and alchemical preparations. The methodology was remarkable for its time: every recipe had to be tested three times, in the presence of witnesses, before it was accepted as valid. Three independent trials with verification. In the 1540s. A century before the Royal Society of London existed.

Ruscelli published the academy’s findings in 1555 under the pseudonym “Alessio Piemontese,” a fictional wandering clergyman from Piedmont. The book, I Secreti, became one of the most successful publications of the entire Renaissance. Over a hundred editions appeared between 1555 and the 1790s. It was translated into French, German, English, Dutch, Spanish, Polish, and Latin. The expanded edition, Secreti nuovi, contained more than a thousand tested recipes.

The book’s success proved something important: practical knowledge, written in Italian rather than Latin, sold. It sold enormously. And it created a template that della Porta would follow three years later, on a grander scale, with more ambition, and with one recipe that would nearly destroy him.

William Eamon, the historian who identified Ruscelli as the real author behind “Alessio Piemontese,” called these books of secrets “intermediaries between the private and esoteric secrets of medieval alchemists and the public Baconian experiments of the seventeenth century.” They were the missing link between medieval alchemy and modern experimental science. At least six similar academies operated in Naples at the same time. The city was a laboratory.

The Boy From Vico Equense

Giambattista was born in 1535 in Vico Equense, a town on the Gulf of Naples. His father, Nardo Antonio della Porta, served Emperor Charles V as secretary for civil appeals. The household attracted visitors: philosophers, mathematicians, royal physicians. Nardo Antonio raised his sons “more as gentlemen than as scholars,” but the informal salon that met in his rooms shaped the boy’s education more than any curriculum.

The tutors were serious. Domenico Pizzimenti, a classicist who had translated Democritus. Donato Antonio Altomare and Giovanni Antonio Pisano, philosophers and royal physicians. An uncle, Adriano Guglielmo Spadafora, supervised the curriculum and pushed the boys toward mathematics and medicine. By fifteen, Giambattista was running his own experiments with magnets and chemicals.

The family owned three properties: the birthplace at Vico Equense, the palazzo on Via Toledo that a relative began building in 1546, and a country estate at Due Porte on the Vomero hills above Naples. “Due Porte” means “two gates,” named for entrances to caverns in the hillside. Those caverns would become meeting rooms for what followed.

Twenty-Three and Dangerous

In 1558, della Porta published Magiae naturalis, sive de miraculis rerum naturalium. He was twenty-three. The book defined natural magic as “the perfection of natural philosophy,” the art of reading the hidden sympathies and antipathies that connected all things. It covered magnetism, optics, alchemy, and strange cures. It was an instant success. Five Latin editions appeared within ten years. Translations into Italian, French, and Dutch followed quickly. By the late 1580s, there were sixteen Latin editions, six Italian, seven French, and two Dutch. Francis Bacon read it. William Gilbert used it. Athanasius Kircher borrowed from it without shame.

But buried in Book II, Chapter 26, under the title Lamiarum Unguenta, “The Witches’ Ointments,” was the recipe that would change everything.

The Recipe

Della Porta published two formulations. The first called for a fat base (traditionally described as children’s fat, boiled in a bronze vessel) mixed with celery-family plants, aconite (wolfsbane), poplar leaves, and soot. The second substituted water parsnip, yellow iris, cinquefoil, bat blood, solanum (nightshade, which della Porta specifically noted “makes you sleep”), and oil.

The application method was precise: warm the skin through vigorous rubbing to open the pores, then work the ointment in for absorption through the skin.

What happened next was the part that mattered. The users fell into a deep, deathlike trance. When they woke, they reported vivid experiences of flying through the air, attending feasts with music, and mating with attractive young men. “They believe they fly through the air on gibbous moon nights,” della Porta wrote. “They see banquets, music, parties.” His explanation was entirely material: the plants contained hidden virtues that penetrated the warmed skin and affected “that part of the brain wherein the memory consists,” filling it with hallucinations so vivid that the dreamers could not distinguish them from reality.

Then della Porta did something that separated him from every other writer on the subject. He tested it.

He and a group of men observed a woman reputed to be a witch as she undressed and rubbed the ointment over her body. She fell into a sleep so deep that shouting, shaking, and even beating could not wake her. When she finally came around, she told them she had crossed seas and mountains. The men insisted she had not moved from the room. They had watched her the entire time. She refused to believe them.

The gap between what della Porta saw (a comatose woman lying motionless on the floor) and what the woman reported (aerial flight across continents) was his proof. The Witches’ Sabbath was not a gathering of devil-worshippers. It was a pharmacological event. The women were not flying. They were drugged.

The Pharmacology Nobody Understood Yet

Della Porta could not have known why the ointment worked. The chemistry would not be understood for centuries. But the ingredients he listed contain some of the most potent psychoactive compounds in the European botanical pharmacopoeia.

The key plants in the recipes belong to the Solanaceae family, the nightshades: belladonna, henbane, mandrake, and black nightshade. All of them contain tropane alkaloids, primarily atropine, hyoscyamine, and scopolamine. Scopolamine is the critical compound. It is one of very few plant alkaloids that can be absorbed directly through intact skin when dissolved in a fat base. Modern medicine uses the same principle: transdermal scopolamine patches for motion sickness exploit this exact property.

At hallucinogenic doses, scopolamine produces true delirium, not the geometric distortions of psychedelics but fully immersive hallucinations indistinguishable from reality. Patients in modern emergency rooms who have been poisoned by scopolamine consistently report the sensation of flying or floating. They interact with people and objects that are not there, with complete conviction. The pharmacological mechanism is anticholinergic: scopolamine blocks muscarinic acetylcholine receptors in the central nervous system, producing sedation, amnesia, and vivid hallucinations.

The aconite in della Porta’s first recipe added another layer. Aconitine, its active compound, causes intense tingling and numbness that spreads from the application site across the entire body. At sub-lethal doses applied to the skin, this creeping paresthesia could plausibly contribute to the sensation of the body lifting off the ground or transforming. Aconitine is also extraordinarily lethal. The estimated fatal dose is two milligrams. Its inclusion in the flying ointment was the most dangerous component.

The fat base was not arbitrary. Fat-soluble alkaloids dissolve into lipid carriers, which then pass through the skin’s lipid barrier. The vigorous rubbing della Porta described would have increased blood flow to the skin’s surface, accelerating absorption. This is essentially the same principle behind modern transdermal drug delivery systems.

The ointment worked because it was, in modern terms, a transdermal delivery system for a cocktail of anticholinergic deliriants. The women who rubbed it on their bodies experienced exactly what modern pharmacology would predict: deep sedation followed by vivid, immersive hallucinations of flight.

Why a Recipe Could Get You Burned

To understand why della Porta’s recipe was dangerous, you need to understand the theological war it walked into.

For centuries, the Church’s official position on witchcraft had been surprisingly moderate. The Canon Episcopi, a church document from around 906 AD incorporated into canon law through Gratian’s Decretum, declared that women who believed they flew through the night sky in the train of the goddess Diana were deluded. The flights were illusions created by the devil. They were not physically real. Anyone “so foolish and stupid” as to believe otherwise was themselves deceived.

This position held for five hundred years. Then it reversed.

In 1487, Heinrich Kramer published the Malleus Maleficarum, the witch-hunting manual that argued witchcraft was real, physical, and effective. Witches really did fly. They really did consort with demons. The Canon Episcopi had to be reinterpreted. Pope Innocent VIII’s bull Summis Desiderantes Affectibus of 1484 gave inquisitorial sanction to this new position. The reversal fueled the witch craze that burned tens of thousands across Europe over the next two centuries.

The legal logic rested on a specific chain: witchcraft involved a conscious pact with the devil. This pact constituted treason against God. Therefore witchcraft was the most serious crime possible, warranting execution. Judges were authorized to use torture freely and convict on circumstantial evidence.

Della Porta’s recipe blew a hole through this chain. If the Sabbath was a hallucination caused by plants, there was no flight. If there was no flight, there was no gathering. If there was no gathering, there was no pact with the devil. If there was no pact, there was no treason against God. If there was no treason, there was no crime. The entire prosecution apparatus collapsed.

Jean Bodin, the French jurist and political philosopher, understood this immediately. In his 1580 De la Demonomanie des Sorciers, he damned della Porta as “un grand Sorcier Neapolitan,” a great Neapolitan sorcerer. Bodin wanted della Porta burned at the stake. His reasoning was twofold: by publishing the recipe, della Porta was spreading the devil’s tools. By explaining the Sabbath as a drug trip, he was providing witches with a defense and undermining the entire apparatus of witch prosecution.

The Jesuit demonologist Martin Delrio repeated Bodin’s condemnation in his Disquisitiones Magicae of 1599, maintaining that witchcraft was genuine and demonic.

But the recipe also had defenders.

The Chain of Citation

In 1563, the Dutch physician Johann Weyer published De praestigiis daemonum (On the Tricks of Demons), one of the first major medical arguments against witch persecution. Weyer used della Porta’s ointment experiment as concrete, empirical proof that the women confessing to flying were not flying. They were sick, deluded, or drugged. They needed treatment, not execution. Weyer still believed in demons, but he did not believe witches had real power from them.

In 1584, the English writer Reginald Scot cited della Porta (referring to him as “Johannes Baptista Neapolitanus”) in The Discoverie of Witchcraft. Scot noted that della Porta’s experiment “greatly undermined the opinion of those who wrote in absolute maintenance of witches’ transportations.”

In 1631, the Jesuit priest Friedrich von Spee published Cautio Criminalis, a devastating attack on witch trials. Spee had personally accompanied condemned women to execution and became convinced they were innocent. He cited della Porta’s ointment recipe as evidence against the claims of Bodin and Delrio. The recipe demonstrated that confessions of flying and sabbath attendance could be explained naturally, which undermined the entire evidentiary basis for burning people.

The chain runs: della Porta (1558) to Weyer (1563) to Scot (1584) to Spee (1631). Each writer used the same recipe as ammunition against the same machine. The recipe was not obscure esoterica. It was a live weapon in a legal and theological war that lasted two centuries and killed thousands.

Della Porta was not the first to describe the flying ointment. Girolamo Cardano discussed it in De subtilitate rerum in 1550, and the Spanish physician Andres de Laguna conducted a famous experiment with it in 1545, testing it on an executioner’s wife who fell into a thirty-six-hour coma and woke up describing erotic adventures. But della Porta’s version was the most detailed, the most widely read, and the most explicitly naturalistic in its conclusions. His was the version that got cited, attacked, and censored.

The Academy of Secrets

The success of Magia Naturalis drew visitors to della Porta’s door. Around 1560, he formalized these gatherings into the Accademia dei Segreti, the Academy of Secrets. Its Latin name was the Academia Secretorum Naturae. It was modeled on Ruscelli’s earlier academy, right down to the name. The admission requirement was straightforward: to join, you had to demonstrate that you had discovered a new secret of nature unknown to the rest of humanity. Each meeting demanded another.

Members called themselves the Otiosi, the “Men of Leisure,” a name that carried aristocratic irony. These were experimenters, physicians, and natural philosophers pooling their findings in a network built on mutual disclosure. The meetings took place at della Porta’s palazzo on Via Toledo and at the family estate at Due Porte, where underground chambers beneath the villa served as meeting rooms. The historian Benedetto Croce visited the Due Porte site centuries later and found archaeological evidence of these subterranean spaces.

A group of men meeting in underground caverns to share “secrets of nature” while their leader was already under suspicion for publishing witchcraft recipes. The Inquisition drew the obvious conclusion.

The Silencing

The trouble began in the early 1570s. Rumors of necromancy reached Rome from Naples. The populace called della Porta “Indovino” (fortune-teller) and “Mago” (magician). Denunciations from fellow Neapolitans followed. In the early 1570s, the Roman Holy Office opened legal proceedings.

Cardinal Luigi d’Este repeatedly invited della Porta to Rome between 1579 and 1587, ostensibly for research but practically to shield him during his ongoing trial. D’Este was della Porta’s patron. Without that protection, the outcome might have been different.

The Academy of Secrets was shut down around 1580 by order of Pope Gregory XIII. The closure was final.

In 1583, Magia Naturalis was placed on the Madrid Index of prohibited books. The specific trigger, according to Neil Tarrant’s research in the British Journal for the History of Science, was della Porta’s naturalistic approach to witchcraft. The flying ointment recipe was the focal point, but the deeper threat was his entire project: explaining seemingly supernatural phenomena through hidden natural causes. This systematically reduced the domain in which demonic explanations were necessary. One faction within the Church understood this as a direct challenge to orthodox theology and embedded their objections in the machinery of censorship.

In 1586, della Porta was summoned before the Neapolitan Inquisition and given a specific instruction: stop publishing on divinatory and magical arts. Write comedies instead.

In 1592, all of della Porta’s philosophical works were banned. In 1593, the Venetian Inquisition prohibited his Italian translation of De Humana Physiognomonia. The ban was not lifted until 1598. By 1585, he had become a lay brother of the Jesuits, devoting one day per week to charitable work at the Ospedale degli Incurabili. Whether this was faith or a condition of his continued freedom is unclear. Probably both.

The Inquisition kept him under lifelong surveillance until his death in 1615.

The Self-Censored Edition

In 1589, della Porta published the vastly expanded second edition of Magia Naturalis: twenty books instead of four. It was an encyclopedia of everything he had learned in thirty years of experimentation. Optics and the camera obscura. Magnetism. Cosmetics. Distillation. Perfumes. Gunpowder. Steelwork. Cooking. Hunting. Invisible writing. Pneumatic devices.

The flying ointment recipe was gone.

Book II, Chapter 26, Lamiarum Unguenta, the chapter that had made him famous and nearly destroyed him, had been removed. When the Italian translator produced his edition, he wrote to readers: “so as not to enflame the curiosity of the impious… we shall silence these compositions.”

The 1589 edition retained chapters on soporific medicines in Book VIII: “To cause Sleep with Mandrake,” “For the same, with Nightshade,” “A Sleeping Apple.” The ingredients were the same. The conclusion was missing. The recipe had been amputated from its meaning.

The 1658 English translation, published in London by Thomas Young and Samuel Speed, was based on the censored 1589 edition. For most English-speaking readers, the flying ointment never existed.

The Rest of Him

Della Porta published over twenty books across more fields than any single person should reasonably have attempted. A few deserve mention.

In 1563, he published De Furtivis Literarum Notis, a treatise on cryptography. His Porta cipher, a polyalphabetic substitution system using thirteen alphabets instead of twenty-six, was self-reciprocal: the same operation encrypted and decrypted. He also proposed hiding messages inside hardboiled eggs, admitted the method did not work (“I put it in vinegar and nothing happened”), and published the failure alongside the recipe. He noted that “eggs are not stopped by the Papal Inquisition and no fraud is suspected to be in them.”

In 1586, he published De Humana Physiognomonia, arguing that human character could be read from physical features by comparison with animals. The illustrations, human heads placed side by side with animal heads in woodcut engravings, became some of the most reproduced images in Renaissance natural philosophy. They also led, through Lavater and Gall, to Cesare Lombroso’s attempt to identify “criminal types” by physical features in the nineteenth century. That line of inheritance is not flattering.

In 1588, Phytognomonica cataloged plant signatures: a walnut resembles a brain, so it heals the head. The concept is associated with Paracelsus, but della Porta was arguably “the real originator of the botanical Doctrine of Signatures in any approximation to a scientific form.” The Phytognomonica was physiognomy applied to the botanical world, and it fit within the Hermetic tradition that saw macrocosm and microcosm as mirrors of each other.

His Pneumaticorum libri duo (1601) described a steam-powered apparatus that anticipated Thomas Savery’s steam engine by nearly a century. His Olivetum (1584) was the first treatise dedicated entirely to olive cultivation.

And then there was the theater. The Inquisition told him to write comedies instead. He became one of the finest comic playwrights of his generation, producing at least seventeen plays while working alongside Torquato Tasso at the court of Cardinal Luigi d’Este. The plays were good enough that Renaissance scholars take them seriously on their own terms. The Inquisition had silenced his magic. It had not silenced him.

The lynx illustration on the title page of the 1589 Magia Naturalis, with its motto about observing nature “with lynx-like eyes,” directly inspired the name and emblem of the Accademia dei Lincei{target="_blank"}, the oldest scientific academy in the world, founded in 1603 by the eighteen-year-old Roman nobleman Federico Cesi. Della Porta was enrolled among the Lincei in 1610. Less than a year later, Galileo joined. The age of natural magic was giving way to mathematical physics. Della Porta belonged to the first age. Galileo to the second.

He died on February 4, 1615, in Naples, in the house of his daughter Cinzia. He was seventy-nine.

The Professor’s Recipe, Tested

In 1960, the German folklorist Will-Erich Peuckert, a professor at the University of Gottingen, did something that no scholar had done in the four centuries since della Porta published his recipe. He made the ointment. He rubbed it on his own skin.

His report: “We had wild dreams. At first, horribly distorted faces danced before my eyes. Then I suddenly had the feeling that I was flying through the air for miles. The flight was repeatedly interrupted by deep dives. In the closing phase, there was an image of an orgiastic party with grotesque sensual excesses.”

Peuckert first mentioned the experiment during a 1959 lecture in Bremen, which generated enormous media interest. He subsequently appeared in a television documentary filmed in the cellar of his own house, preparing della Porta’s ointment. The experiment confirmed what della Porta had observed four hundred years earlier: the recipe produced experiences that matched the historical accounts. Sensations of flight. Erotic visions. The absolute conviction that the experience was real.

The danger of della Porta’s explanation was never that it was wrong. The danger was that it was testable. And when tested, it worked.

What the Professor Left Behind

The institutional lineage from della Porta’s work runs in a clear line. Ruscelli’s Accademia Segreta in the 1540s. Della Porta’s Accademia dei Segreti in the 1560s. The Accademia dei Lincei in 1603, named after della Porta’s lynx. The Accademia del Cimento in Florence in 1657, the first academy dedicated explicitly to experimental science. The Royal Society of London in 1660. The professors of secrets, with their insistence on testing recipes rather than citing authorities, were the direct ancestors of experimental science. William Eamon called their books “the missing link between medieval secrets and Baconian experiments.”

His contemporary Giordano Bruno burned for his ideas. Della Porta survived by bending. He submitted to the Inquisition, joined the Jesuits, wrote comedies, and kept experimenting in private. Bruno got a statue in Campo de’ Fiori. Della Porta got a hotel on Via Toledo. Only one lived long enough to keep working.

His colleague Isabella Cortese published her own book of secrets in 1561, three years after Magia Naturalis, centered on alchemy, perfumery, and cosmetics. She was part of the same Neapolitan tradition, the same movement of professors of secrets who insisted that knowledge came from experience rather than authority.

The Philosopher’s Stone eluded him, as it eluded everyone. The alchemical tradition he documented, stretching back through Hermes Trismegistus and Zosimos of Panopolis, lives on in every chemistry lab that owes its origins to a furnace and a flask.

The palazzo on Via Toledo still stands. The underground rooms at Due Porte have been documented by archaeologists. The lynx that della Porta put on his title page still watches from the crest of Italy’s national academy. The recipe he was forced to cut from his book has been restored by modern editors. Four hundred years after his death, the Professor of Secrets has outlasted most of the people who tried to silence him. His recipe works. It always did.