She prophesied by "singing the fates" and writing on oak leaves arranged at her cave's entrance; if the wind scattered them she would not reassemble the prophecy. The entrance to Hades lay at nearby Avernus; Aeneas sought her before descending to meet Anchises' shade. She warned that the descent is easy but the return labour indeed, then guided him through the underworld as a liminal bridge between living and dead.

Though mortal, Ovid's Sibyl lived about a thousand years. Apollo offered a wish for her virginity; she took a handful of sand and asked to live as many years as the grains. When she later refused his love he withheld eternal youth: her body withered, was kept in an ampulla, and at last only her voice remained — a fate compared to Tithonus. Petronius's Satyricon has Trimalchio claim he saw her hanging in a jar at Cumae, answering the boys' "Sibyl, what do you want?" with "I want to die."

Roman tradition has an old woman offer nine books of prophecy to King Tarquin; refused, she burns three and offers six at the same price, then three more, until he buys the last three at the original sum and she vanishes. The books were kept in the Capitoline Temple of Jupiter, consulted only in emergencies, lost in the fire of the 80s BC, and later reconstituted; Augustus moved them to Apollo's temple on the Palatine.

Christians read Virgil's Fourth Eclogue and the Sibylline Oracles as messianic; Augustine quoted the Oracles, Dante took Virgil as guide, and Michelangelo placed the Cumaean Sibyl among the prophets on the Sistine ceiling. T. S. Eliot's Waste Land opens with Petronius's jar; Mary Shelley framed The Last Man as leaves found in the Sibyl's cave.