Freud wrote in Civilization and its Discontents (1929) that “the problem of preservation in the human mind” could be visualized by thinking about Rome, a city in which ancient structures and events seem so active in the present that we can “see” them when we look at the modern city Rome has become. Freud starts from the view, that “in mental life nothing which has once been formed can perish-that everything is somehow preserved and that in suitable circumstances … it can once more be brought to light” (16).2 He imagines Rome as “a psychical entity … in which … all the earlier phases of development continue to exist” alongside the latest one:

This would mean … On the Piazza of the Pantheon we should nd not only the Pantheon of today, as it was bequeathed to us by Hadrian, but, on the same site, the original edice erected by Agrippa. … And the observer would perhaps only have to change the direction of his glance or his position in order to call up the one view or the other. (Freud 17)

Although he explores it at length, this idea strikes Freud as fantastical. For those of us with access to twenty rst century interactive visual data sites, however, it hardly seems far-fetched. Almost a century after Freud’s thoughtexperiment, today we can explore visual images digitally. Using a computer mouse or a keystroke, we can shift the physical perspective from which we see any given image. More impressively, we can trace the history of images of a particular object or place, seeing evidence of different historical moments in any order we wish … or even simultaneously.