“La véritable différence est que les Pythies de l’oracle apollinien ont été des femmes réeles et les Sibylles, des êtres imaginaires comparable aux nymphes ou aux muses/The real difference is that Apollo’s Pythian prophetesses were actual women, while the Sibyls are imaginary beings comparable to nymphs or muses.”
The Sibyls were legendary ancient Greek prophetesses whose unsolicited oracular pronouncements were written, as epic and didactic poetry usually were also, in dactylic hexameter verse. Among the Greeks in classical and Hellenistic times the Sibyls were held in prestige second only to Apollo’s oracle at Delphi. At the same time, Sibylline oracles were accorded even higher honors in Rome: an officially sanctioned collection of them was kept in the temple of Jupiter Optimus Maximus, where they were consulted in times of emergency by a board of certified interpreters, the quindecemviri.
The earliest extant reference to Sibylline prophecy, from Heraclitus (6th/5th century bce) as quoted in Plutarch’s De Pythiae Oraculis (1st century ce), mentions only one Sibyl, and already she is a shadowy figure of hoary antiquity: “Think of the elegance of Sappho’s songs, that so charm and fascinate the listener! Σίβυλλα δὲ μαινομένῳ στόματι καθ’ Ἡράκλειτον ἀγέλαστα καὶ ἀκαλλώπιστα καὶ ἀμύριστα φθεγγομένη χιλίων ἐτῶν ἐξικνεῖται τῇ φωνῇ διὰ τὸν θεόν/And contrast the Sibyl, who, from her madwoman’s lips, as Heraclitus tells us, speaks words without laughter, without adornment, without perfume, and reaches through a thousand years with her voice because of the god”. The exact extent of the quotation is unclear — does it include μαινομένῳ στόματι/“from her madwoman’s lips” and does it run from ἀγέλαστα/“without laughter” to φθεγγομένη/“who speaks” or to τὸν θεόν/“the god” or to somewhere in between? — but even if we assign the reference to a thousand years to Plutarch, the Sibyl will still already have been only a figure of hearsay to Heraclitus, as she clearly was also to Aristophanes and Plato.
 Nikiprowetsky, Troisième Sibylle, 1.
 The most comprehensive recent treatment of the Sibyls is Parke, Sibyls and Sibylline Prophecy; see pp. 136-51 and 190-215 on the official Roman collections.
 Plutarch, De Pythiae Oraculis 397A; translation by Russell, Plutarch: Selected Essays 62, with internal quotation marks omitted.
 See Aristophanes, Equites 61, Pax 116 and 1095; Plato, Phaedrus 244b, Theagenes 124d.