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Cecilia Powell has identified the subject of this sketch as the town of Nemi above the lake of the same name.1 Turner’s viewpoint is from the opposite side of the lake, at a spot to the south-east of the town of Genzano. The panorama continues on the opposite sheet of the double-page spread, see folio 22 verso, (D15336).
For a general discussion of Turner’s view of Lake Nemi see folio 19 (D15329).
Powell 1984, p.422.