This subject comes from Virgil’s poem, the Aeneid. The Trojan hero, Aeneas, has come to Cumae to consult the Sibyl, a prophetess. She tells him he can only enter the Underworld to meet the ghost of his father if he offers Proserpine a golden bough cut from a sacred tree.
Turner shows the Sibyl holding a sickle and the freshly cut bough,in front of Lake Avernus, the legendary gateway to the Underworld. The dancing figures are the Fates. Like the snake in the foreground, they hint at death and the mysteries of the Underworld, amidst the beauty of the landscape.