Ah, Stonehenge. This ancient rock monument has attracted the fascination of archaeologists and historians ever since John Aubrey gave it a once-over back in the 17th century.

And it doesn't take long to list some of the biggest questions we've always had about it. Where did these rocks come from? How did they get there? Who put them together like this? And, perhaps most curious of all, why?

Well, it's taken a lot longer to answer these questions than it has to ask them, but Mike Parker Pearson and his associates have nailed down a very important piece of the puzzle that will make it a lot easier to answer the questions that remain.

His newest article in the archaeology journal Antiquity shows compelling evidence that we've finally got a fix on the origin of the Stonehenge rocks, which are the key to its greatest mysteries.

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1. But Pearson's team didn't just pull the answer out of thin air.

No, the general origins of many of Stonehenge's rocks have been known for a while now. In fact, the monument's larger stones, composed of a sandstone known as sarsen, can be traced to a 20-mile radius of Salisbury Plain, where Stonehenge is located. And even the smaller "bluestone," types found there weren't a total mystery. Even back in the '20s, those could be traced to the Preseli Mountains in western Wales. But the recent discoveries are a little more specific.
Joel Sartore | National Geographic

2. Thanks to the discovery of ancient bluestone quarries like this one in 2011, now we know exactly where the stones are from.

The most dominant bluestone types in Stonehenge are spotted dolerite, which can be found in Carn Goedog, and what's called "rhyolite with fabric," which is the star of the show at Craig Rhos-y-felin. It's through this Welsh site that we learn exactly how the megaliths, or giant stones used for making monuments, found themselves in Stonehenge.
Mike Parker Pearson et al. | Antiquity/Cambridge University Press Irene de Luis
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3. So what's so special about the quarry at Craig Rhos-y-felin?

Well, if you take a look at the marked area in this 1954 photo from Stonehenge...
Mike Parker Pearson et al. | Antiquity / Cambridge University Press English Heritage

4. You might notice that it's a match for the rock marked "11" in this photo.

This confirms that the rhyolite found here is the same type as in Stonehenge, which means that a significant part of the monument was brought from 140 miles away. And when you consider when it happened (between 3100 and 2920 BC) that's quite an amazing feat. 
Mike Parker Pearson et al. | Antiquity/Cambridge University Press Adam Stanford