The depth of history at Queen Anne's Gate - a handsome Baroque street overlooking St James's Park - is unusual even in London, and few houses resonate with more memories than the extraordinary number 14. The story of the house over the centuries features political revolutionaries, occult initiations, clandestine war meetings, and a decapitated head. It begins, however, as a museum of Roman sculpture, unrivaled outside Italy, designed for connoisseur and virtuoso Charles Townley (1737-1805). Townley embodied Enlightenment values perhaps more completely than any other figure in the art world of...