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The term "prehistoric" is used for those objects and incidents that were produced/occurred in times before these were coded through written records or any other kind of manmade record that would allow the following generations to build a continuum of information - a coherent narrative -  about the past.

So prehistoric art refers to objects that were made and used by people who did not leave precise records about their history, or whose records were lost. As a consecuence, there is a narrative void between them and modern day history, which started with the appearance of the first writing systems. Note that therefore, as scripture didn't appear everywhere at the same time, while in some places history was already being recorded, in other regions you still had "prehistoric" conditions.

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Cheers,

Papitou 

Art from along time ago