A Twelfth-Century Text on the Number Nine and Divine Creation: A New Interpretation of Boethian Cosmology?

Psalteries of the Royal Door Gate (1144) of the Cathedral of our Lady of Chartres

“…In the twelfth century Magister Johannes of Seville in his Liber Alchorismi de pratica aritmetice, translation of the lost book of Muhammad ibn Musa al-Kwarizmi, introduces the Indian numeration. He explains that "ergo constat unumquemque limitem 9 numeros continere", he recalls that nine are the celestial spheres and nine the angelic choruses [2]. William of Conches in his work Philosophia gives no importance to the Ten, while nine are the invisible circles of heaven (Liber II, V, 13) and nine months of human gestation (Liber IV, XIV, 22-23).…”