Mathematical Theologies uncovers the lost history of Christianity's encounters with Pythagorean religious ideas before the Renaissance. David Albertson shows that the writings of Thierry of Chartres (d. 1157) and Nicholas of Cusa (d. 1464) represent a robust Christian Neopythagoreanism that reconceived the Trinity and the Incarnation within the framework of Greek number theory. Their sophisticated mathematical theologies challenge contemporary assumptions about the relation of religion and modern science. David Albertson surveys the slow formation of Neopythagorean theologies of the divine One from the Old Academy through Middle Platonism into the Middle Ages. Against this backdrop, Thierry of Chartres's writings stand out as the first authentic retrieval and incorporation of Neopythagoreanism within western Christianity. By reading Boethius and Augustine against the grain, Thierry reactivated a suppressed potential in ancient Christian traditions that harmonized the divineWord with notions of divine Number. Despite fame during his lifetime, Thierry's ideas remained well outside the medieval mainstream. Nicholas rediscovered anonymous fragments of Thierry and his medieval readers, and drew on them liberally in his first mystical treatise. Yet tensions among this collection of sources drove Cusanus to try to reconcile their competing understandings of Word and Number. Over three decades Nicholas eventually learned how to articulate traditional Christian dogmas within a Neopythagorean cosmology of mathematized nature - anticipating the situation of modern Christian thought after the seventeenth century. Mathematical Theologies skillfully guides readers through the newest scholarship on Pythagoreanism, the school of Chartres, and Cusanus, while revising some of the categories that have separated those fields in the past.