Art as we know it began in 1790 or thereabouts. Anything earlier that we might think of as art has to be declared to be art by a gesture similar to how a readymade is appointed. That's not my theory, and I don't think it needs to be taken too seriously, but I just posted a brief history of art and a reminder of my call for mail art exchange at the Needle's Haystack:
https://ristoid.substack.com/p/short-lesson-art-history