Bk 1. xxv. Epistolary codes (Caesar cipher)

(detail) Brit. Lib. Harley MS 3035 f.11v


Suetonius is our authority for the ‘Caesar cipher’:

“If he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet, that not a word could be made out. If anyone wishes to decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others.” – Suetonius,  Life of Julius Caesar 56

  • Technically the Caesar cipher is a ‘shift cipher’. Neatly described in English and in ‘mathematik’ at Learn Crytography.com  [HERE].  That page includes a tool for encryption and decryption of Caesar-cipher messages.
  • A good clear short (2 min 35 sec) history and explanation in a video from the Khan Academy. Treats the cipher’s various forms and long use, and explains how its weakness was described by al-Kindi, eight hundred years later. [HERE]
  • A tool to translate  hexidecimal ciphers to the simpler Caesar cipher [HERE] – courtesy of CRYPTII.
  • The current wiki article ‘Caesar Cipher’ isn’t too bad either. [HERE]


We have some  (unencrypted) letters written by, or to Caesar – not in the original, but as they were relayed by others.  Not all such ‘Letters to Caesar’ are accepted as genuine, but the ones in Cicero’s collected writings are.

  • Adolf F. Pauli, ‘Letters of Caesar and Cicero to Each Other’, The Classical World. Vol. 51, No. 5 (Feb., 1958), pp. 128-13. (JSTOR)
  • Jeffrey Tatum, A Caesar Reader: Selections from Bellum Gallicum and Bellum Civile, and from Caesar’s Letters, Speeches, and Poetry. (2012).
  • ‘On the State’ – a letter to Caesar attributed to Sallust.  Transcriptions from the Loeb edition’s parallel Latin and English are linked paragraph by paragraph, at The Lacus Curtius site  [HERE].  

Historically dubious or openly fictional:


in Old French

  • You can read it online [HERE] courtesy of Pennsylvania University’s Lawrence J. Schoenberg Library (LJS MS 421).  The Library also provides an ebook download [HERE], but  no pdf option.  Slides of all the library’s manuscripts available as e-books [HERE].  btw – Dot Porter appears in these listings as an author of extraordinary range and longevity 🙂

Hippocrates’ letter in Occitan

  • Ms.: Princeton, Garrett 80, ff. 9v-14r (seconda parte); ff. 23v-31v (prima parte).
  • Ms.: Auch, Archives départementales du Gers I 4066, ff. 67r-68v; 72v-73r; 77r-v;69r-71r.

I am indebted for the last two references to Nick Pelling’s blog ciphermysteries (September 4th., 2010).

2. Artemidorus to Caesar
  • A fictional letter in Shakespeare’s play Julius Caesar, Act 2, Sc.3.

3. Letter to Caesar from the King of the Britons
  • Geoffrey of Monmouth recounts it, as a letter he believed (or said he believed) written to Caesar by  “Cassibellaunus, king of the Britons”.  See Geoffrey’s History of the Britons, Bk. IV, ch. 2.

4. Letter from Pontius Pilate to Caesar.
  •  Said by its publishers, McIntosh and Twyman to have been in the “Archo Volume” – ie the archives – in Constantinople and in records of the Senatorial Docket, (quote) “taken from the Library at Rome”. (which ‘library at Rome’ is unclear; Rome contains a fair number).  The letter purports to describe in detail the arrest and crucifixion of Jesus Christ, though we do not have evidence that the circumstances surrounding any individual’s execution in this way was a subject of international correspondence with the emperor.  The Romans are estimated to have killed at least a million persons by crucifixion. One instance and perhaps the largest mass crucifixion saw 6,000 set by Crassus along the Appian way after the rebellion of Spartacus.    However, here’s a  pdf of the ‘Pontius to Caesar’.

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