If Britain’s prehistoric monuments have had a magnetic attraction for generations of artists, it is perhaps because they have long been seen as works of art themselves. ‘The whole temple of Avebury may be consider’d as a picture’, enthused the antiquary William Stukeley in 1743, while ‘my God how sculptural’ was Barbara Hepworth’s response to Cornish sites such as the Mên-an-Tol and the Nine Maidens which she encountered after moving to St Ives in 1939.