Whilst browsing /r/astronomy , someone posted a collection of their telescope photos, including a "mandatory shot of the moon". That got me thinking about how all these photos of the moon these amature astronomers take are a lot of evidence for the moon's existance, in a wierd technical kind of way.
That got me thinking, what's the ealiest piece of historical evidence (pictures, writing, etc) that the moon exists?
One could easily imagine if the Earth lost its moon 3000 years ago somehow, written records would be a big reason we'd ever know today that it was there in the first place.
Well, the oldest known texts are Sumerian, which is also the oldest known writing system that we can still read. And the Sumerian texts are full of reference to the moon - you can do a full-text search of (a translation of) the sumerian corpus here - there are multiple references to the moon in Ninurta's Exploits, for example.
I would be very surprised if there aren't multiple depictions of the moon in various forms of pre-historic art as well (I know of one theory that the cave paintings in Lascaux contained a lunar calendar, for example) but I'm not an archeologist so I can't really speak to that.