vulgat.) Marbode admitted that herbs have great power, but the virtues of gems are
greater. Some people may question their powers, but only because powerless imitation
gems have misled them. The sapphire, for example, preserves a person from fraud, envy,
and terror and can release a captive from prison. An amulet made of gagates (“jet”) works
against dropsy, while fumigation with this stone is effective against both epilepsy and
demons. Indeed, gagates can even counteract magical illusions and incantations.
Magnetite, which Circe used in praestigiis magicis, can be used to test the fidelity of
one’s wife: place it against her head while she is sleeping, and if she has been chaste she
will embrace you, while if she has committed adultery she will tumble from the bed. A
burglar can force all occupants from a house by sprinkling burning coals on the floor and
then adding crushed magnetite.
Through the 12th century, medieval writers relied heavily on Isidore of Seville’s
Etymologiae for discussion of magic and its various forms: Rabanus Maurus (in his De
magicis artibus), Hincmar of Reims, John of Salisbury, and others drew from Isidore, and
the survey of magic at the end of Hugh of Saint-Victor’s Didascalicon stands in this
tradition of antimagical literature. Hugh says that magic is “false in what it professes,
mistress of every iniquity and malice, lying about the truth and truly harming souls,
seduces them from divine religion, promoting the worship of demons, encouraging the
corruption of morals, and impelling its followers’ minds to every crime and wickedness.”
He then goes on to divide magic into its branches: mantice includes necromancy and
divination by the four elements, mathematica is the use of horoscopes and other
divinatory devices, sortilegium is casting of lots, maleficium uses demonic incantations
and ligatures ostensibly for healing, and praestigium deceives the senses by demonic art.
Perhaps the most important theorist of magic in medieval France was William of
Auvergne, a theologian and then (from 1228 to 1249) bishop of Paris, who discusses
magic extensively, especially in De universo 2.3.18–25, and De fide et legibus 24 and 27.
William presents himself as a pioneer in this area, claiming with slight exaggeration that
he has found nothing relevant in earlier writers. What surely is true is that he is the first
important theorist in the high Middle Ages to articulate a conception of magic allowing
for natural as well as demonic forms. He is also important because in his early years he
read widely in the writings of the magicians and astrologers themselves and thus had a
clear idea what they were attempting to do.
Like other writers, William recognizes that a great deal of magic is demonic. He tells
of one necromantic experiment entitled the Major Circle, in which demon kinds from the
four cardinal directions come with retinues of horsemen, musicians, jugglers, and so
forth. Another such experiment produces a phantom castle. The magicians may claim
they are invoking good spirits, but William is convinced that the angels used are fallen
ones, demons who live in the sublunary air and in desert regions (to which magicians
often have recourse). He tells how magicians have young boys gaze into mirrors or other
reflective surfaces, and after conjurations have been recited some such mediums (perhaps
as few as one out of ten) will see apparitions. Plato explained this effect in terms of the
soul being turned back on itself so that its own power of divination is enhanced, and
William conceded that explanations of this sort were possible, yet he inclined to suppose
that demons were generally at work in such magic.
William is more original in recognizing a natural magic—“the part of natural science
that is called natural magic” (De universo 2.3.21) as an alternative to the demonic sort.
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