the time of the persecutions, has long been discussed. The fragments of the Philosophy from Oracles are only quoted by Christians, especially Eusebius, Theodoret, Augustine, and John Philoponus. The fragments contain oracles identifying proper sacrificial procedure, the nature of astrological fate, and other topics relevant for Greek and Roman religion in the third century. Whether this work contradicts his treatise defending vegetarianism, which also warned the philosopher to avoid animal sacrifice, is disputed among scholars. Against the Christians (Adversus Christianos) During his retirement in Sicily, Porphyry wrote Against the Christians (Κατὰ Χριστιανῶν; Adversus Christianos) which consisted of fifteen books. Some thirty Christian apologists, such as Methodius, Eusebius, Apollinaris, Augustine, Jerome, etc., responded to his challenge. In fact, everything known about Porphyry's arguments is found in these refutations, largely because Theodosius II ordered every copy burned in AD 435 and again in 448. Augustine and the 5th-century ecclesiastical historian Socrates of Constantinople, assert that Porphyry was once a Christian. Other subjects Porphyry was opposed to the theurgy of his disciple Iamblichus. Much of Iamblichus' mysteries is dedicated to the defense of mystic theurgic divine possession against the critiques of Porphyry. French philosopher Pierre Hadot maintains that for Porphyry, spiritual exercises are an essential part of spiritual development. Porphyry was, like Pythagoras, an advocate of vegetarianism on spiritual and ethical grounds. These two philosophers are perhaps the most famous vegetarians of classical antiquity. He wrote the (Περὶ ἀποχῆς ἐμψύχων; De Abstinentia ab Esu Animalium), advocating against the consumption of animals, and he is cited with approval in vegetarian literature up to the present day. Porphyry also wrote widely on music theory, astrology, religion, and philosophy. He produced a History of Philosophy (Philosophos historia) with vitae of philosophers that included a life of his teacher, Plotinus. His life of Plato from book iv exists only in quotes by Cyril of Alexandria. His book Vita Pythagorae on the life of Pythagoras is not to be confused with the book of the same name by Iamblichus. His commentary on Ptolemy's Harmonics (Eis ta Harmonika Ptolemaiou hypomnēma) is an important source for the history of ancient harmonic theory. Porphyry also wrote about Homer. Apart from several lost texts known only from quotations by other authors, two texts survive at least in large parts: the Homeric Questions (Homēriká zētḗmata, largely a philological comment on the Iliad and Odyssey) and On the Cave of the Nymphs in the