The classic text on ruins is Edward Gibbon’s The Decline and Fall of the Roman Empire, completed during the last decades of the 18th century, when the English were cultivating a special interest in historical empires that their own advancing empire might yet surpass — a compensatory preoccupation brought on by the recent loss of the American colonies. Toward the end of his massive opus, Gibbon contemplates what it would have been like to “discover” Rome in that late medieval moment when the great metropolis was first appreciated as a ruin.