For those who prefer a little bit of history and intrigue with their occult references and celestial nomenclature, this is a pure gem of the mystic literary world.
Trithemius is best known for his Steganographia, but he penned several shorter, less well known works, including this work here, which refers to the history of the world (as envisioned by Renaissance era christians!) as being split up into mathematically stable periods of time, each ruled by one of several angelic forces, each also representative of a celestial body; Anael, Raphael, Gabriel, and so forth. Each of these forces has its own nature during its reign, and Trithemius compares historical events within each of these periods to the same- noting the changing of rulership, the development of culture, and the rise and fall of empires.
In the near future I will also edit and release two of Trithemius' other shorter works; the Steganographia will have to wait for the future, being a true "full length" manuscript.