Abu l-Walid Muhammad ibn Ahmad ibn Muhammad Ibn Rushd (520-95/1126-98, Averroes in the Hispano-Latin tradition) defended philosophy by returning to the text of Aristotle. In his secular effort to explain and to revive the true doctrine of Aristotle, cosmology took a place of special importance. In his Commentarium Magnum on Aristotle's book 'On the Heavens', one of Ibn Rushd's later works, he encountered the essential rationalism of Hellenistic philosophy where reason is actual and visible in the reality of the cosmic order. The concepts and principles of this cosmology, and especially the philosophic dogma of the eternity of the world, were among the most significant contentious issues of medieval philosophy. Thus, it is hardly surprising that this literal commentary on the full text of the Aristotelian work was made available in Latin as one of the earliest translations of Ibn Rushd's works.