The building is inspired by the Grotto of Egeria. Clérisseau drew this subject a number of times: almost identical versions are in the Royal Collection, Windsor Castle, in the Robert Hull Fleming Museum, Burlington, Vermont and in the Louvre dated respectively 1763, 1764 and 1765, see T.J.McCormick, Charles-Louis Clérisseau and the Genesis of Neo-Classicism, Cambridge, Mass., 1990, pp.120-4