In the midst of reading Robert Graves' I, Claudius [1], I was surprised to encounter a description of an interesting cipher used by the fictional Augustus. I therefore thought it would be worthwhile to write a short article to draw attention to what is perhaps not a particularly well-known cipher appearing in fiction. I will assume that the reader is familiar with the principle behind the famous Vigenère cipher (see [2] or [3]).

In the novel, Claudius, as narrator, relates how, upon Augustus' death, he is succeeded somewhat reluctantly by his stepson Tiberius, due to the machinations of Livia, who was Augustus' widow and Tiberius' mother. As her son's imperial reign begins, it is clear that Livia intends to hold on to the influence that she wielded during her husband's.