4to.  [10] + 394 + [2] pages; fold-out table. 201 x  158 mm. Modern half leather over original parchment binding.

Trithemius’ most controversial work was his unfinished treatise on “steganography” (cryptography), set aside around 1500 and not printed until 1606, though it circulated in manuscript form. Trithemius was not the first monk to be intrigued by codes; we possess some letters by Pachomius, fourth-century Egyptian leader of the cenobitic (communal) monastic movement, written in a code that still has not been broken. It was not Trithemius’ interest in codes so much as his teaching on the conjuring of angelic spirits as intermediaries between sender and recipient that got him into trouble. He also cloaked his teaching with all the trappings of an esoteric cult, including oaths of secrecy and deliberately obscure discussions of the technique. Like many in his day, Trithemius had a lively belief in angels, demons and other spirits, and sought to use their energies to advance Christian theology. This aim was analogous to his insistence that Classical learning and secular subjects were useful, indeed necessary, adjuncts to theological inquiry.

The Steganographia contains examples of encryption in which a secret message is hidden within a “plain message” that makes its own sense when read literally. More problematic is the addition of a secret sign that indicates which spirit is to be invoked to aid the transcription, and more problematic still is the assertion in Book Three that messages can be sent entirely via such intermediaries without any written text at all. The page shown illustrates a message in plain sense (a letter of recommendation), then the spell that will alert the recipient to the code being used (the spell was indicated by a cryptic symbol), and finally, at the bottom of the page, the intended secret message: “Beware this person, for he is an evil man and has nothing good to say.” 

Saint John’s Rare Book Collection. Formerly in the library of John Jebb (1775-1833), Church of Ireland (Anglican) Bishop of Limerick, Ardfert and Aghadoe. Acquired June 2000.