In the Gesta regum anglorum (ca. 1125), William of Malmesbury, an Anglo-Norman monk and historian, interrupted his history of the kings of England with a lengthy digression on Gerbert of Aurillac, the scholar, teacher, and bishop who became Pope Sylvester ? (999-1003). Gerbert was a controversial figure: lauded for his erudition, piety, and care for his students during his lifetime, after his death he became known as a medieval Faust - a nefarious pope and fallen monk whose intellectual concupiscence led him to practice necromancy and divination for personal gain.1 One of the most persistent legends refers to a prophetic head that he created to learn his own destiny. According to William, Gerbert used astral science and observation to make his oracular statue.
After a careful observation of the stars (that is, at a time when all the planets were beginning their paths again), he cast for himself the head of a statue that could speak, if questioned, and answer the truth in the affirmative or the negative.2
Legends about Gerbert and his talking head had circulated for at least fifty years before William's early twelfth-century account, often conjoined to stories of how he had learned the impermissible arts of necromancy in Muslim Spain, and had summoned the Devil in order to enter into a diabolical pact. William repeated, embellished, and changed some aspects of Gerbert's biography, while adhering to the main elements of the narrative. According to William, Gerbert acquired the knowledge and skill to create his oracular head during a lengthy sojourn in Seville. After growing up in the Cluniac monastery of Saint-Géraud, Gerbert escaped the strictures of monastic rule to pursue his education. "[E]ither bored with monastic Ufe or smitten with a desire for glory, he fled one night to Spain, intending primarily to learn the science of the stars and others of this kind of art from the Saracens."3 It was
[t]here he conquered Ptolemy in knowledge of the astrolabe, Alhandreus in the positions of the stars, Julius Firmicus in prophesying. There he learned what the song and flight of birds portended, there he learned to summon ghostly forms from hell; there he learned everything that is either harmful or healthful that has been discovered by human curiosity; but on the permitted arts, such as arithmetic, music, and astronomy, and geometry, I need say nothing. By the way he absorbed them he made them appear beneath his ability, and through great effort he recalled to Gaul those subjects that had been long obsolete. He was truly the first to snatch the abacus from the Saracens, and gave the rules for it that abacists, for all their intelligence, hardly understand.4
William's description of Gerbert's intellectual achievements, including the talking head, is more detailed than some of the earlier versions recounted by chroniclers and polemicists. These details reveal important distinctions between conceptions of legitimate and illegitimate knowledge, and between established doctrine and new ideas. In his account, William emphasized that Gerbert learned what was permitted and what was prohibited. The subjects of the quadrivium - music, arithmetic, geometry, and astronomy - were a traditional part of a liberal arts education since late antiquity. Necromancy - summoning "ghostly forms from hell" - and augury - from birdsong and flight patterns - fell far outside the bounds of accepted intellectual practice. Yet William did not likewise condemn celestial divination - prophecy based on careful observation of heavenly bodies and their positions. Careful inspection of the skies, the use of astronomical instruments, and mathematics were central to astral science, one of the subjects of the quadrivium. It is important to note that the modern distinction between astrology and astronomy is not visible in medieval terminology, although celestial observation and prediction were differentiated conceptually and in practice in this period. …