The Geomantic Constellation in the Middle Ages: Social Dissemination and Doctrinal Debates (Thomas Aquinas, Roger Bacon, Peter of Abano, Engelbert of Admont, and Augustinus of Ancona)

From the 13th century onward, the widespread use of geomantic practices in various contexts of medieval society and the proliferation of a substantial corpus of treatises and compilations are closely interrelated phenomena. Unsurprisingly, after the translation and dissemination of early geomantic Arabo-Latin treatises in the 12th century and the composition of original texts on geomancy in Latin in the 13th century, medieval thinkers began to scrutinize this divinatory art in terms of its effectiveness, permissibility, origin, relationship with astrology and other forms of divination, and its anthropological and moral implications, as part of the broader debate on divination that emerged in the 13th and 14th centuries. Moreover, the doctrinal analysis of the geomantic method and its theoretical presuppositions and practical implications represents only one aspect of a far more complex phenomenon. To assess what geomancy really was and how it was perceived in the Middle Ages, it is necessary to consider literary sources, condemnations and legal documents, social contexts, and political actors: taken together, all these elements form what can be defined as the geomantic constellation of the Middle Ages. In this contribution, I have focused on a number of works written over a span of about forty years by five authors with different intellectual backgrounds: the Dominican Thomas Aquinas, the Franciscan Roger Bacon, the Benedictine monk Engelbert of Admont, the Augustinian Hermit Augustinus of Ancona, and the physician Peter of Abano. From this overview, it becomes clear that, despite significant differences, all these texts share common characteristics: a. They demonstrate a first-hand knowledge of technical geomantic literature or deep familiarity with well-informed sources about the geomantic method; b.They address all or some of the three central topics of the medieval doctrinal debate on geomancy (the epistemological status of geomancy and its relationship with other forms of prognostication; whether geomantic divination is linked to demonic interventions or is a natural technique; and the psychological dimensions of the geomancer and the consultant); c. Some of these texts also suggest that geomancy was a form of divination rooted in medieval society and culture, alluding to its dissemination among prominent scholars (Bacon) and its ecclesiastical condemnation (Engelbert of Admont and Augustinus of Ancona). We owe Thomas Aquinas fundamental elements that would characterize the subsequent debate on geomancy, such as the notion of superstitio divinativa and the view that demons take advantage of the geomantic procedure to deceive men (‘Summa theologiae’), as well as the tendency to emphasize the peculiarities of geomancy compared to other divinatory techniques (‘De sortibus’). Overall, Thomas has a nuanced attitude towards geomancy, since on the one hand he rejects its underlying conceptual model (astral determinism) and emphasizes that fortuitous events cannot be predicted, but on the other he shows a good knowledge of this divinatory technique and insists that the procedure involves silencing the higher faculties. Bacon, who writes shortly after Thomas, is extremely negative towards geomancy, considering it one of the species of false mathematics, a form of ceremonial magic based on conjuration of demons and implying astral fatalism. Furthermore, he argues that geomancers use astrological notions, implicitly suggesting that this astrological conceptuality serves to conceal their dealing with demons. A more positive approach is adopted by Peter of Abano, who embraces Magister Speculi’s conception of geomancy as one of the garamantiae, recognizing that it is form of divination provided with a solid theoretical foundation. He is even willing to admit experiencing geomantic judgments that proved correct. Engelbert of Admont, who refers to geomancy to clarify the mechanism of fascination, does not take the ecclesiastical prohibition as proof of falsity of the geomantic judgment. Augustinus of Ancona places his analysis at the epistemological level and, after an in-depth comparative analysis between astrology and geomancy, recognizes the limited reliability of geomancy; in line with Thomas, however, he argues that it is not appropriate to resort to the geomantic method, since it offers the devil the opportunity to deceive human beings.