What is the theme in The Cantos by Ezra Pound?

A palimpsest, most simply, is a piece of paper or parchment that has been written on a number of times and on which the earlier writing has been only partially effaced. But the term also designates a building that incorporates an earlier building, especially one from a previous historical period. The image of the palimpsest is both a structural principle for The Cantos and one of its most important themes.