Trithemius, the abbot who hid secrets among the angels

Johannes Heidenberg, known as Trithemius from the Latin name of his birthplace, Trittenheim on the Moselle, was born in 1462 and died in Würzburg in 1516. He was Benedictine abbot of Sponheim, a tireless bibliophile, historian and theologian. To posterity, however, he has remained above all as the father of modern cryptography and, at the same time, as a suspected magician. Both reputations are tied to the same book, the Steganographia.

A book that spoke of spirits

Trithemius worked on the Steganographia around 1499 and the work circulated for a long time only in manuscript. On the surface it is a treatise on angel magic: it teaches how to call upon spirits with resounding names, each linked to a direction or an hour, so that they may carry messages over a distance. Contemporaries were already troubled by it, and when the text was finally printed in Frankfurt in 1606 the Church placed it on the Index of Forbidden Books a few years later, in 1609.

In reality, at least in the first two books, the long formulas of invocation conceal enciphered messages: the meaningful letters are arranged according to precise rules among words without sense. The angelic disguise served to protect the method, but also, perhaps, to stress that for Trithemius every secret communication had an almost spiritual dimension. The third book, made of astrological tables, was recognised as a cryptographic system only in the 1990s.

The Polygraphia and the square table

The case of the Polygraphia, published in 1518, is different. Here Trithemius openly sets out several systems of encipherment. The most famous is the so-called Ave Maria cipher, in which every letter of the message is replaced by a Latin word, so that the ciphertext looks like a devout prayer. The same book contains the tabula recta, a square table of progressively shifted alphabets, which lies at the origin of the polyalphabetic ciphers developed in the following decades.

The Polygraphia also contains a collection of exotic and magical alphabets, among them the letters that would become famous as the Theban alphabet. Trithemius presents them beside scripts attributed to ancient kings and sages, in a collection that blends erudition and fantasy. In the same vein stands another of his historical works, in which he reconstructed the origins of the Franks from chronicles that nobody has ever been able to trace.

Agrippa's master

In 1509 or 1510 the young Heinrich Cornelius Agrippa visited Trithemius, then abbot in Würzburg, and dedicated to him the first draft of the De occulta philosophia. The abbot's letter of reply, which survives, is an invitation to caution: certain secrets should be shared only with a few trusted friends. Through Agrippa, many alphabets collected or described by Trithemius passed into the great encyclopaedia of Renaissance magic.

The reputation of a magician followed Trithemius even after his death. Stories circulated that he had summoned for the Emperor Maximilian I the spirit of his late wife, Mary of Burgundy, a legend the sources do not confirm but which contributed to his myth. In the seventeenth century the Jesuit Athanasius Kircher and other scholars discussed the Steganographia at length, some defending it as a work of cryptography, others condemning it as a book of necromancy.

In the figure of Trithemius the learned monk, the cryptographer and the explorer of the occult live side by side. Separating these aspects is difficult, and perhaps it would make no sense: for him hidden writing was a single field, in which technique and mystery supported each other. His legacy can be found as much in the cipher manuals of European chanceries as in the libraries of devotees of magic.