 The 6th century witnesses at once the culmination and the demise of a long tradition of philosophical commentaries on the works of Plato and especially Aristotle. This tradition already began in the 1st century BCE, but it becomes first tangible for us with the commentaries on Aristotle of Aspasius in the 2nd century CE and especially with Alexander of Aphrodisias in the early 3rd century. This exegetical tradition reached its pinnacle in the first half of the 6th century with the great works of Ammonius Hermeiou and his pupils Simplicius and John Philoponus. The latter was a Christian who, after much criticism and polemic, broke with (pagan) Neoplatonic school philosophy and turned his energy to the exegesis of biblical texts as well as the theological controversies of his day. However, because of the survival of even later commentaries attributed to philosophers with Christian names such as Elias and David, it is commonly supposed that in the later 6th century pagan philosophy was indeed still being taught in Alexandria, only by Christians. This would then be in marked contrast to Athens, where pagan philosophy died out rapidly after the Athenian academy was closed by Emperor Justinian in 529.