 Porphyry was a prolific author who wrote about a whole range of topics. There are some sixty works attributed to him, but most of them are now lost or survive in mere fragments. Extant (though not all complete) are: Life of Plotinus, Life of Pythagoras, Letter to Marcella, On Abstinence from Eating Food from Animals, Starting-points Leading to the Intelligibles (usually called the Sententiae; in Latin the work is called Sententiae ad intelligibilia ducentes), the Isagoge (Introduction), On the cave of the Nymphs, Introduction to Ptolemy’s opus quadripartitum (see Bezza 2012) and there are commentaries on Ptolemy’s Harmonics and Aristotle’s Categories. An extant work attributed to Galen, To Gaurus, is almost certainly by him. There are fragments of a history of philosophy and fragments of a number of works on psychology. One such work, the Symmikta zetemata, has been partly reconstructed by Heinrich Dörrie (1959). It has been argued by Pierre Hadot (1968 and several articles) that Porphyry is the author of anonymous fragments of a commentary on Plato’s Parmenides. This attribution has been widely accepted but also forcefully challenged (see below). He also wrote commentaries on Plato’s Timaeus and several works by Aristotle. The fragments of these are given in Smith 1993, which contains the extant fragments and testimonia of Porphyry. In addition we know that Porphyry wrote on such diverse subjects as grammar, philology, rhetoric, and geometry. Against the Christians is perhaps Porphyry’s best known title. Of this large work only some fragments have survived.