The Steganographia of Trithemius: angels, spirits and hidden messages

In 1499 a letter threw an abbot's reputation into crisis. Trithemius had written to his Carmelite friend Arnold Bostius describing a work in preparation which, he claimed, could transmit thoughts at a distance without words or visible signs. Bostius had died before the letter arrived, and the text was read by others, who saw in it the promise of magical powers. Thus was born the disturbing fame of the Steganographia.

A scandal foretold

Rumours spread quickly. The French philosopher Charles de Bovelles, who visited Sponheim in the early years of the sixteenth century and was able to leaf through the manuscript, wrote that he had found in it invocations of spirits and barbarous names, and accused the author of demonic magic. Trithemius defended himself by maintaining that the work dealt with natural secrets, but he chose not to publish it. The text remained unfinished and circulated in manuscript copies.

The affair weighed on Trithemius's memory for a long time. When he left Sponheim after disputes with his monks, his reputation as a necromancer was already established, and popular tales credited him with wondrous feats, such as making the spirit of Emperor Maximilian's late wife, Mary of Burgundy, appear before him. These are legends, but they clearly show the image that had formed around him.

The trick of the first two books

The Steganographia presents itself as a manual for communicating with the help of spirits, each with a name, a rank and a sphere of competence. To send a message one would supposedly have to recite formulas addressed to these spirits. In reality, in the first two books the formulas themselves are ciphered texts: they contain instructions for hiding a message in an apparently innocent letter, for instance by taking only certain letters of each word.

The term steganography, which Trithemius coined by combining the Greek words for “covered” and “writing”, denotes precisely this practice: not making the message incomprehensible but hiding the very fact that it exists. The angelic apparatus worked as a further screen, and perhaps as a form of learned irony towards the naive reader. In the seventeenth century the Spaniard Juan Caramuel y Lobkowitz and other scholars defended its cryptographic nature.

The mystery of the third book

The third book, shorter and left unfinished, seemed different. It contains tables of numbers linked to the planets and to planetary spirits, without the keys that accompany the earlier books. For centuries it was regarded as proof that Trithemius really practised astral magic. The work was printed only in 1606 in Frankfurt and shortly afterwards was placed on the Index of Prohibited Books.

In the 1990s two scholars, the Germanist Thomas Ernst and the mathematician Jim Reeds, showed independently that the tables of the third book also conceal ciphered texts. Once the key is applied, the numbers yield short and entirely ordinary Latin sentences, like exercises. Even the book thought to be the most magical turned out, at least in part, to be a disguised manual of cryptography.

The Steganographia holds a unique place among Renaissance books. For some readers it was a grimoire, for others a riddle, for others again a learned joke. Today it stands as evidence of how thin, in Trithemius's time, the boundaries between the science of signs, magic and the art of secrecy were, and how constantly they were debated.