The subject of this sketch is the Rocca Pia in Tivoli, a massive fortress with four crenallated towers, built by Pope Pius II in 1461.1 Turner’s viewpoint is from the south side of the castle and to the left can be seen 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. Visible in the middle distance on the left is the Church of Santa Maria Maggiore and the Villa d’Este, whilst to the right is the campanile of the Cathedral (Duomo) San Lorenzo. 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.