  Al-Kindi’s corpus includes several treatises on cosmology, explaining and defending a picture of the cosmos as four concentric circles of elements, which are mixed together by the outer, heavenly spheres to yield complex compound substances like minerals, plants, and animals. Though al-Kindi’s main influences are works of Aristotle and his commentators, especially Alexander, he also knows something of the Timaeus, as is shown by a treatise explaining why Plato associated the elements and heavens with the Platonic solids (Abu Rida 1953, 54–63; also Rescher 1968).