"In Ancient times, messages were inscribed on parchement or tabets. When a particular message had served it's purpose, the surface of the parchment would be wiped and, reinscribed with a new message. But the elimination of the original message was not always throughly effective, and often parts of the old message would show through. The new message would have to be read over and around the remaining older messages. The term 'palimpsest' is used to describe this reinscription of new messages over, alongside and around earlier messages."
pal·imp·sest n. 1. A manuscript, typically of papyrus or parchment, that has been written on more than once, with the earlier writing incompletely erased and often legible. 2. An object, place, or area that reflects its history: “Spaniards in the sixteenth century... saw an ocean moving south... through a palimpsest of bayous and distributary streams in forested paludal basins” (John McPhee).
[Latin palimpsstum, from Greek palimpsston, neuter of palimpsstos, scraped again : palin, again; see kwel-1 in Indo-European Roots + psn, to scrape.]