Charlemagne's Cipher

While writing my recent article on the Theban Alphabet I was pleasantly surprised by something I recognized from my childhood. Like many young boys I was fascinated by Kings, knights, and crusades. This fascination sometimes crossed with my other interests, like codes and ciphers.

This cipher is the one Charlemagne used to pass messages to his generals. The cipher can easily be found in cryptography and cryptology books at your local library, but it may also be found in Johannes Trithemius' Polygraphia (1518).