The Cumaean Sibyl

The Cumaean Sybil was the most famous of of the Sybils, the prophetic old women of Greek mythology; she guided Aeneas through Hades in the Aeneid. She had been granted immortality by Apollo, but because she forgot to ask for perpetual youth, she shrank into withered old age and her authority declined. (NA)

see also

 

sources
Norton Anthology, vol II