The most familiar Euclid is Euclid of Megara who devised the basic theorems of geometry that all school children used to be obliged to learn. Honorius, the author of the Sworn Book is referred to as the son of Euclid of Thebes (probably the Thebes in Greece not that of Egypt). This is not the same Euclid, but a more shadowy figure who may well have originally written in Greek.

The book opens with the mention of a convocation or meeting at which 811 Masters of magic assemble to decide how to resist a papal plan to persecute magicians. This meeting, which caused the Sworn Book to be written, drew its adepts from as far afield as Athens, Tholetus [Toledo) and Naples, the later city being where the convocation was held.

The Sworn Book was written by Honorius at the request of this group of 811 Master Magicians, to preserve their secrets, and allegedly with the help of the angel Hocroell. Even at this point we see magicians soliciting the help of angels in intellectual endeavour, a theme that will continue to repeat itself over the next 800 years. The date of composition of this grimoire is definitely before 1249, and most likely date being during the papacy of Gregory IX (1227-41) a pope who attempted to suppress magic and persecute magicians, as he saw them as a threat to the authority of the church. They were a threat because they purported to converse directly with angels!

Three centuries later John Dee owned a copy of the Sworn Book, and undoubtedly drew upon it for the design of his key sigil, the Sigillum Aemeth. Perhaps it was also the source of the idea that prayers made to the angels could result in communication from beings with superior knowledge and intelligence.

It is also very suggestive that John Dee gave his first public lectures on Euclid of Megara, and in fact contributed a Mathematical Preface to the first edition of Euclid which he helped translate (with Henry Billingsley) and publish in English in 1570. Euclid resurfaces much later in 1651, when significantly a certain Captain Thomas Rudd (1583-1665) published just the first six books of the geometry of Euclid of Megara together with the same Preface by John Dee.

Both Rudd and Dee (who owned a copy) would have been familiar with the Sworn Book of Honorius son of Euclid of Thebes. Is it possible that their interest aroused in Euclid of Megara may have initially been caused by a confusion of this Euclid with the Euclid of Thebes?

In Dee’s efforts to get intellectual satisfaction from the angels, piety and cleanliness were paramount considerations. This grimoire stresses the purity of its intent, and not just in order to preserve its owners from possible ecclesiastical prosecution. In the opening paragraphs it says “it is not possible that a wicked and unclean man could work truly in this art; for men are not bound unto spirits, but spirits are constrained against their will to answer clean men and fulfil their requests.” This is a very important point. And later it explains that “we call this book the Sacred or Sworn Book for in it is contained 100 sacred names of God and thus [it is] sacred, for it is made of holy things…it was consecrated by God.”

For Dee, the Sworn Book was very important. It was not just concerned with the invocation of angels, but was the origin of the Sigillum Aemeth (or Sigil of Truth) that is the key diagram engraved on the wax tablets used on his Table of Practice, and on the wax tablets used as supports under its legs. This Sigil, which has a complex geometry, and should be coloured according to very specific rules, may even pre-date the Sworn Book. It also appeared in one of Kircher’s books. The Sworn Book is therefore a prime example of a grimoire which provided the basic rationale, equipment, diagrams and techniques of angel magic.

The Sworn Book was very influential amongst a wider circle of Elizabethan intellectuals, and it is interesting to note that Ben Jonson (1573-1637), the playwright contemporary of Shakespeare, was also the owner of one of the main surviving manuscript copies of The Sworn Book. It is well known that Jonson was interested in and well informed about alchemy, which can be seen from the detail in his play The Alchemist. However it is not so well known that he was also interested in and practiced the angel magic contained in the Sworn Book.

Giordano Bruno visited Dee, and probably read his copy of the Sworn Book when he was in England in the early 1580s, actually incorporated into his book on the Kabalah, a character called ‘Onorio’ from Thebes: probably a sly reference to Honorius of Thebes.