A reluctant innovator: Greco-Arabic astronomy in the Computus of Magister Cunestabulus (1175)

This article is dedicated to the obscure Computus of Magister Cunestabulus (England, 1175), which offers a unique spotlight on the way the twelfth-century ‘Renaissance’ in mathematical astronomy impacted the Latin computistical tradition. Armed with an unusually broad array of sources newly translated from Arabic, among them Ptolemy’s Almagest, Cunestabulus applied his advanced knowledge in the service of traditional Latin learning and established Church doctrine, defending the non-existence of Antipodeans in the southern hemisphere as well as the astronomical foundations of the ecclesiastical computus. His intricate explanation of the error underlying the Julian calendar, which was based on the Arabic theory of the ‘access and recess of the eighth sphere’, makes for a technically sophisticated and conceptually intriguing case of Graeco-Arabic science being used for apologetic ends in twelfth-century Latin writing.