The subject of this faint outline sketch is the Rocca Pia at Tivoli, a massive fortress with four crenallated towers, built by Pope Pius II in 1461.1 The study depicts the castle from the east with the largest tower in the background on the left. Faintly indicated in the bottom left-hand corner are the arches of the Acquedotto Rivellese, a sixteenth-century aqueduct built by Cardinal Ippolito II d’Este to supply water to the Villa d’Este. The aqueduct was demolished at the beginning of the twentieth century. Further views of the Rocca Pia can be found on folio 68 verso, 74 verso–76, 82 verso, 83 verso (D15055, D15065–D15069, D15082, D15084; Turner Bequest CLXXIX 68a, 73a–5, 81a, 82a). As a young man, Turner made copies of related views by other artists, see Dr Monro’s Album of Italian Views (Tate D36453 and D36454; Turner Bequest CCCLXXIII 40).
Compare a watercolour by Friedrich Horner (1800–1864), Il Castello di Tivoli 1850, reproduced in colour in Silvia Visino, I Pittori del Grand Tour: Viaggio a Roma alla ricerca delle aure, Latina 1994, no.55, p.90.