 According to Diogenes Laertius, Parmenides composed only a single work (D.L. 1.16). This was a metaphysical and cosmological poem in the traditional epic medium of hexameter verse. The title “On Nature” under which it was transmitted is probably not authentic. The poem originally extended to perhaps eight hundred verses, roughly one hundred and sixty of which have survived as “fragments” that vary in length from a single word (fr. 15a: “water-rooted,” describing the earth) to the sixty-two verses of fragment 8. That any portion of his poem survives is due entirely to the fact that later ancient authors, beginning with Plato, for one reason or another felt the need to quote some portion of it in the course of their own writings. Sextus Empiricus quotes thirty of the thirty-two verses of fragment 1 (the opening Proem of the poem), though apparently from some sort of Hellenistic digest rather than from an actual manuscript copy, for his quotation of fr. 1.1–30 continues uninterruptedly with five and a half verses from fragments 7 and 8. The Alexandrian Neoplatonist Simplicius (6th c. CE) appears to have possessed a good copy of the work, from which he quoted extensively in his commentaries on Aristotle’s Physics and De Caelo. He introduces his lengthy quotation of fr. 8.1–52 as follows: “Even if one might think it pedantic, I would gladly transcribe in this commentary the verses of Parmenides on the one being, which aren’t numerous, both as evidence for what I have said and because of the scarcity of Parmenides’ treatise.” Thanks to Simplicius’ lengthy transcription, we appear to have the entirety of Parmenides’ major metaphysical argument demonstrating the attributes of “What Is” (to eon) or “true reality” (alêtheia).