Heinrich Cornelius Agrippa’s manual of learned magic, De occulta philosophia (1533), explicated the ways in which magicians understood and manipulated the cosmos more systematically than any of his predecessors. It was here that he mapped the entire network of forces that passed from angels and demons, stars and planets, downward into the world of matter. Agrippa laid his work out in three books, on the elementary, astrological, and celestial worlds. But he saw all of them as connected, weaving complex spider webs of influence that passed from high to low and low to high. With the zeal and learning of an encyclopedist imagined by Borges, Agrippa catalogued the parts of the soul and body, animals, minerals, and plants that came under the influence of any given planet or daemon. He then offered his readers a plethora of ways for averting evil influences and enhancing good ones.¹ Some of these were originally simple remedies, many of them passed down from Roman times in the great encyclopedic work of Pliny the Elder and less respectable sources, and lacked any deep connection to learned magic.

Magic usually required the use of objects charged with power, and Agrippa’s book also offered a massive taxonomy of magical animals, plants, and stones, with ample instructions for their preparation and use. Sufferers from sore throat read in Agrippa that they could cure themselves by touching their necks to the hand of someone who had died prematurely. Those plagued by coughs learned to put spit in the mouths of green frogs and then let them escape.² Reading the book resembles walking through a vast princely chamber of wonders or a grand apothecary’s shop, ceiling, walls, and shelves hung with strange and thrilling creatures.

Chapter after chapter of Agrippa’s work, accordingly, turned into a magnificently encyclopedic if associatively organized mountain of material, partly drawn from written sources and partly from oral tradition and current practice, as the author applied his scissors and paste to the fruits of his vast reading and vaster curiosity. When contemporary readers opened the book at random, as they often did, they would find themselves stumbling into a vast cabinet of curiosities, whose contents Agrippa described with energy and economy:

They say also that a stone bitten by a mad dog has the power to cause discord, if it is put in a drink, and that one who puts a dog’s tongue in his shoe, under his big toe, will not be barked at by dogs, especially if it is added to the herb of the same name, cynoglossa [dog’s tongue]. And a membrane from the afterbirth of a dog has the same effect, and dogs will shun one who has a dog’s heart. And Pliny reports that there are red toads that make their home in briars, and are full of sorcery and do wonderful things. For the small bone that is in its left side, when cast into cold water, makes it immediately become hot. It restrains the attacks of dogs. Added to a drink, it arouses love and quarrels. When tied to someone, it arouses lust. On the other hand, the little bone that is in the right side cools hot water, and it will not become hot again unless the bone is taken out. It cures quartan fevers, when tied in a fresh lamb’s skin, and prevents other fevers and love and lust. And the spleen and heart of these toads make an effective remedy against the poisons that are drawn from those animals. All this Pliny narrates.³

Any reader could find something of interest in this paroxysm of parataxis, a good bit of it taken directly from Pliny and none of it explicitly verified by anything resembling a test. Some of the time, at least, Agrippa served his readers as little more than a source of the homeliest of anecdotes and practices — which they both appreciated and, presumably, recycled in their turn. But sometimes readers indicated that they had tested the claims made by Agrippa and his ancient sources, or seen them tested, by practitioners who knew how to manipulate powerful things. The Benedictine monk Heinrich Duden, for example, liked Pliny’s story, which he read in Agrippa, about how the bone from the left side of a toad could make water hot or inspire love. He treated it, unexpectedly, not as a factoid that had already made an illustrious career passing from notebook to notebook but as a description of a familiar process. After underlining the two relevant bits of the sentence, he wrote: “I saw this done once.”⁴

Even the little toads and their littler bones, moreover, were framed in a larger explanatory system, one that led the reader upward and outward. In classificatory chapters that dealt with the elements, the temperaments, the planets, and the zodiac, Agrippa made it clear that celestial influences shaped each being and object on earth, endowing it both with its powers and with the external marks that revealed these to the skilled eye of the magus. No one could hope to master the occult philosophy, in other words, without mastering the higher studies of astronomy and astrology. The magus also had to have the personal gifts and formal training that would enable him to interpret dreams and prophecies and the knowledge of mathematics required to detect the Pythagorean number patterns that gave the universe structure. In the end, moreover, he needed asceticism and self-discipline since the consummation of his art involved communication with angels. The most graphic parts of Agrippa’s work, the sections most densely involved with the powers of particular bones and plants, provided him with opportunities to introduce larger and more abstract themes that he could then pursue in the second and third books, as he moved on to describe in detail the powers of planets, angels, and daemons.

Agrippa, moreover, interspersed the homely segments of his work with materials of very different kinds, also drawn from diverse provinces of the country of magic. When he evoked the terrifying images of horses’ heads that certain special lamps and candles, made from the liquid exuded by copulating mares, could project, he was once again quoting Pliny, and Pliny in turn was quoting older sources. To judge from Duden’s note, however, preserved in the manuscript he began reading in 1550, Agrippa also described a contemporary magical practice: “I myself have experienced this, with great terror.”⁵ When Agrippa described how witches could catch the eyes of their victim and, by projecting “darts or strokes”, induce fear, love, or misery in them, he recalled the descriptions of witches’ behavior in the book he loathed, Heinrich Kramer’s Malleus maleficarum, and the normal beliefs of contemporary churchmen — as Duden noted when he wrote “a certain witch did this to the executioner at Hamburg in my time.”⁶

The therapies on offer in Agrippa’s book often required the invocation of celestial or angelic powers, either to awake the slumbering, hidden forces of the magical things he wished to manipulate or to protect magus and clients against the more frightening sorts of supernatural powers. Agrippan magic, accordingly, regularly involved direct efforts to invoke the intervention of planetary daemons and other spirits. Talismans, carved from particular substances and engraved with particular signs; magic squares, which revealed the marvelous properties of numbers; and the names of angels, obtained by Christian Cabalistic methods of substitution and recombination — these, among other means too numerous to mention, would enable Agrippa’s readers to change themselves and the world for the better.⁷

Many of the practices Agrippa described in De occulta philosophia came directly from the magic that unfrocked clerics had practiced for generations. Albrecht Dürer’s Melencolia I has made one case in point famous. In this engraving, a magic square — the series of numbers from one to sixteen, arranged in the proper order in a square with sixteen cells — invokes the power of Jupiter, a beneficent planet, against the devastating influence of Saturn. Magic squares like this originated in the Arabic world, long before Agrippa’s time. Often they had their top row of cells filled with the letters of a divine name or with the first letters of a verse from the Koran, and the lower rows with permutations on them. Since Arabic letters, like Hebrew, have numerical values, each magic square automatically forms a mathematical figure, and it was in this form that they became most popular in the West.

The square in Melencolia I starts in the inverse way, with numbers that could turn into letters. If you take a square and enter the numbers from 1 to 16, you obtain the series that follows:

        4 3 2 1
        8 7 6 5
        12 11 10 9
        16 15 14 13

If you then leave half the numbers in place and rotate the other half by 180, the magic square of Jupiter falls into shape:

        4 14 15 1
        9 7 6 12
        5 11 10 8
        16 2 3 13.

“They say”, Agrippa explained, “that if this magic square is stamped on a silver plate at a time when Jupiter rules, it provides profit and wealth, grace and love, peace and concord with men, and placates enemies, confirms honors and dignities and counsels. And if it is inscribed on coral, it destroys evil spells.”⁸ He illustrated the magic squares of the other planets, explained the “characters” that each of them could generate, and described their functions. The great Warburgian scholars Erwin Panofsky, Raymond Klibansky, and Fritz Saxl noted the correspondence between Agrippa’s text and Dürer’s print in the 1920s, and made it one of the foundations of their massive study of Saturn and melancholy.⁹

Dürer, however, did not find his magic square in Agrippa’s book, which would not be published until twenty years after he made his print. It came, rather, from one of the medieval magical texts that, centuries before Agrippa, explained the magic squares and connected each of them to one of the seven planets. The Book of Angels, preserved in a fifteenth-century manuscript now in Cambridge, gives instructions on how to draw down the power of Jupiter that resemble Agrippa’s own directions, though they are even more precise:

When you wish to practice magic with this figure, take a thin piece of silver made on its day (Thursday) and hour, and let Jupiter be in a favorable position. And on the piece sculpt this figure, and suffumigate it with aloe wood and ambrosia, and carry it with you. All who see you will love you, and you will succeed in whatever you ask of them. And if you put this figure between the feet of merchants, their business will grow. And if you put it in a dovecote or in a place where bees are gathered, they will thrive.¹⁰

Like this particular set of rules and numbers, much of the concrete material Agrippa assembled could be, and often was, found elsewhere. When he explained how to charge rings with power that could defend their owners against illness — by inscribing them with images, names, and characters, suffumigating them, and choosing astrologically propitious times for doing so — he named practices that were described in detail by numerous texts and objects that were familiar to the many consumers of magical objects, from the Holy Roman emperor on down.¹¹

But few of the dozens of manuscript compilations that transmitted magic through the Middle Ages reflected any effort to impose a system on the whole range of magical practices, as Agrippa’s book did.¹² He made clear that each of the separate arts of magic, from the simplest form of herbal remedy to the highest forms of communication with angels, fitted into a single, lucid structure with three levels: the elementary or terrestrial realm, ruled by medicine and natural magic; the celestial realm, ruled by astrology; and the intellectual realm, ruled by angelic magic.¹³ Long tendrils of celestial and magical influence stitched these disparate realms into something like a single great being:

For inferiors are joined to their superiors in such a way that an influence proceeds from their head, the first cause, like a string stretched taut, down to the lowest things of all. If one end of this string is touched, the whole immediately shakes, and a touch of this kind resounds all the way to the other end. The motion of the inferior makes the superior move as well, to which the other corresponds, like the strings in a well-tuned lute.¹⁴

Characteristically, Agrippa developed this passage over time, adding the last clause as he polished his work for publication. Duden savored its eloquence, and wrote appreciatively in his margin about this “beautiful and apt comparison.”¹⁵ But it was more than that. The magician, Agrippa showed, uses his knowledge of the powers of natural things to master and ascend from the elementary world. He draws on mathematics and astrology to pass through the celestial spheres. And he finally achieves full and true knowledge of God by carrying out ceremonial magic.

The magus could trace lines of influence upward along the great celestial power grid of the universe and downward into every order of being on earth:

All the stars have their own natures, properties, and conditions, and through their rays, they also produce signs and characters in inferior beings as well, in the elements, in stones, in plants, in animals and their members. Therefore each thing receives from its harmonic disposition and its star that irradiates it a certain special sign or character, which is stamped on it, which refers distinctively to that star or harmony, and has a power differing from all the rest either in genus, or species, or number of the preexisting material. Thus each thing has its mark, for some special effect, stamped on it by its star.¹⁶

Agrippa offered, in other words, both a grand, schematic plan of the cosmos, rather like that of the London Underground, which laid out its structure as a whole, and a clutch of minutely detailed local Ordinance Survey maps, which made it possible to navigate through any specific part of the cosmos. Readers rapidly saw what Agrippa had to offer. The owner of a copy of On Occult Philosophy, now in Munich, made clear in his only annotation that he appreciated Agrippa’s systematic presentation of a universe in which physical forms revealed the natures of beings and their relations to one another: “Physiognomy, metoposcopy [the interpretation of faces], and chiromancy, and the arts of divination from the appearance and gestures of the human body work through signs.”¹⁷ Agrippa’s book not only became the manual of magical practice, but it also made the formal claim that magic was a kind of philosophy in its own right.