@brianjakub,
Well if you've ever been to Stonehenge you know that stamped on the bottom of each and every Sarsen Stone is the inscription: "These stones erected in 3,402 B.C."
...but if you're serious then I don't have any evidence whatsoever. I've never been to Stonehenge, and for all I know there is no such structure. You're getting into a pretty murky area here in that we can't really know anything about anything we don't have personal experience of. If you want to follow that course then every source is unreliable and in order to know anything we have to find out for ourselves.
Earlier you asked if Stonehenge and the universe were natural occurances. In a way, yes. We are a part of the natural world, so any of our works are as well. And why not? Isn't a spiderweb or a bird's nest a natural occurance? Then why not the Leaning Tower of Pisa and "To Kill a Mockingbird"?