Yeah I've done a little bit of research and no one knows for sure, there's a buncha different theories.
However.. I think one of the most popular is that it's sort of a sun wheel to help them know when to plant crops and stuff, but.. Really.. I dunno. When I look at it I think of a portal. :D Or.. Some kind of astronomical phenomena.. Or.. Infinity. Who really knows.. That's one thing with a lot of this ancient symbolism.. It's mostly guess work. Some people like to think they know, but who really knows unless you have a direct path to that knowledge and I'm not sure how that's possible when it goes back so far. Even if you were a member of a secret society with a lot of hidden information.

Also yeah. I tend to agree.
I think the guys with weird heads remind me a lot of like grey aliens, I think it's very likely they could have been real beings they saw!