Roger Bacon (Image from Maier, 1617)
Medieval mathematicus Roger Bacon considered the manipulation of numbers to be an art that all serious scholars of the occult should master. Michael Maier included Bacon, a.k.a. Doctor Mirabilis, in his book of famous magicians.
Obsession with secrecy, often in the form of codes and symbols, is characteristic of all magicians. Many, such as Roger Bacon believed the relationship between all things could be best expressed using numbers. Bacon described maths as a mystical and magical art - a sentiment with which many of us might well agree.The first serious Renaissance work on number codes is Polygraphiae written by German monk Johannes Trithemius and published in Cologne in 1564. One of the codes in Polygraphiae was used by the Hermetic Order of the Golden Dawn, a secret society that heavily influenced Victorian and modern European occultism. (Aleister Crowley a.k.a. The Great Beast, was a member.)
Renaissance code created by Johannes Trithemius. People were suspicious of him and his codes. (Image from Trithemius, 1564)