"Was conjured by that pitiless Erictho"

(Canto 9, line 23)

Erictho was a Thessalian witch figuring in Lucan's "Pharsalia" who possessed the power to call souls back from the dead. On the eve of the great battle of Pharsalus, she summons one of the dead to deliver a prophecy of the end of the battle to Pompey's son Sextus. In book 6 of the Aeneid, where the Sibyl leads Aeneas through the underworld, she points out to him that it was Hecate, the goddess of witchcraft, who first guided her through those domains. Dante's poem evokes Virgil's narrative at this point, and is taken as some as a demonstration by Dante that he didn't believe in the idea, widely endorsed during the Middle Ages, that Virgil himself had been a master of witchcraft.