The hunt for the origin of eighteenth-century Romanticism, Kenneth Clark wrote, is “a favourite sport among art historians.” Is it the dark and stormy night in June 1764 when Horace Walpole dreams that he is in the hall of an ancient castle, sees a giant armored hand on the topmost banister of the staircase, then wakes up and starts writing The Castle of Otranto? Or is it the months between the Lisbon Earthquake of 1755 and the publication of Burke’s inquiry into the fearful Origins of the Sublime in 1756?

Clark proposed Piranesi’s Carceri d’Invenzione, mostly designed in 1745, and first published in 1750. The Imaginary Prisons, Clark wrote, are “an extraordinary prelude” to the Romantic “imagery of fear.” There is, however, an earlier image of Romantic fear and reason run amok. In October 1720, Alexander Pope obtained a license to dig a tunnel under the road that separated his house and garden at Twickenham, west of London; the site of Pope’s villa, demolished in 1808, is now only ten minutes’ walk from Walpole’s restored Strawberry Hill. Extracting, as Dr. Johnson put it, “an ornament from an inconvenience,” Pope expanded the central section of the tunnel into a grotto, a “luminous Room, a Camera Obscura, on the walls of which all the objects of the River, Hills, Woods, and Boats, are forming a moving Picture . . . it is finished with Shells interspersed with Pieces of Looking-glass in angular Forms . . . at