If, as the flaneurs claimed, walking around Paris is an art, then the city itself is the surface on which they create. And since Paris is ancient, that surface is not blank. Artists paint over their old work or that of others, just as medieval scholars scraped back the surface of vellum or parchment to use it again. Such a sheet, called a palimpsest, bears faintly, however often it’s reused, the words of earlier hands. And we who walk in Paris write a new history with each step. The city we leave behind will never be quite the same again.
–John Baxter, The Most Beautiful Walk in the World