I had the opportunity to watch a little bit of a National Geographic show, Stonehenge Decoded, narrated by good old Donald Sutherland. The show relates the theory of the archeologist Mike Parker Pearson that Stonehenge was in fact a place of the dead. Upon discovering large post holes on the edge of fields around Stonehenge and the cremated remains of several scores of people he theorized that Stonehenge was sacred ground reserved for the dead.
Its an interesting theory, but much like the theory that some Phoenicians came to Briton to show them how to build the thing it seems to be a whole lot of theory without too much evidence. We don't know why those bodies were burned and buried and probably never will.
As for Stonehenge, we continue to marvel at the abilities of our ancestors for reasons that escape me. We are the same animal as they, same brain size, same cognitive abilities, they just didn't have the benefit of 3 million years of tool building behind them. They built stone henge wit stone and wooden tools, sweat and a lot of back breaking hard work. They learned from experience, building smaller stone circles and over time perfected their craft until some designer figured out how to do it with really big stones.
No aliens. No Magic. It was the power found in the human back.
How do I know this. I've watched games of Minecraft and I've seen it done! ;)