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As Cecilia Powell first identified, the subject of this sketch is Lake Avernus, a volcanic crater lake near Pozzuoli, which is represented in classical mythology as the entrance to the underworld.1 This view looks south across the lake towards the Bay of Baiae and the promontory of Cape Misenum (present-day Capo Miseno). On the eastern shore is a Roman ruin known as the Temple of Apollo. The prospect was very well known to Turner. He had already painted two oil compositions of the vista prior to seeing it for himself: Aeneas and the Sibyl, Lake Avernus circa 1798 (Tate N00463); and Lake Avernus: Aeneas and the Cumaean Sibyl circa 1814–15 (Yale Center for British Art),2 both of which are based upon a drawing by Sir Richard Colt Hoare (1758–1838), who also commissioned and owned the latter picture.3 A related pencil study can be found in the Turner Bequest (Tate D02381; Turner Bequest LI N). Lake Avernus is also the setting for a later oil painting, The Golden Bough exhibited 1834 (Tate N00371).4
Despite his familiarity with Lake Avernus, Turner made several on-the-spot sketches which are scattered throughout the Gandolfo to Naples sketchbook, see folios 19 verso, 34 verso–35, 71–72, 77–78 (D15592, D15622–D15623, D15695–D15697, D15707–D15709; Turner Bequest CLXXXIV 19a, 33a–34, 69–70, 75–76). This particular study disrupts an unrelated sequence of views of the Bay of Gaeta. A small part of the composition spills over onto the opposite sheet of the double-page spread, see folio 28 (D15609; Turner Bequest CLXXXIV 27).