"guarding the door of Darkness"
Aeneas, the Sybil and Charon (c. 1700)
Public DomainAeneas, the Sybil and Charon (c. 1700) - Credit: Giuseppe Maria Crespi

An allusion to the Cumaean Sibyl, the priestess who presided over the Apollonian oracle at Cumae.

In Roman mythology, an entrance to the Underworld was said to be located at Avernus, a crater lake near Cumae. In Virgil's Aeneid, the Sibyl guards 'the door of gloomy Dis' – the door of the Underworld into which Aeneas is to descend.