When was Stonehenge built?

Stonehenge is one of those things that sounds like it’s not going to be very impressive — basically a bunch of rocks in a circle — but is actually kind of amazing.

That’s probably, at least in part, because of the mystery behind those who built it. The culture responsible left no written records, so we’re left to fill in the landmark’s origins with whatever fantastical ideas we come up with. The fact that the stones are aligned to the sunset of the winter solstice and the opposing sunrise of the summer solstice only deepens the mystical vibe.

But all that mystery hasn’t stopped us from trying to figure it all out, and we’ve actually been able to come up with some solid hypotheses on when the main structure was built. How old is Stonehenge?