People have long tried to unravel the mysteries of Stonehenge. The circle of massive stones in England's Wiltshire county may be one of the world's most famous prehistoric sites. But there are some questions that still nag archaeologists. Namely, when was it built exactly and why?

Listen to our interview with Timothy Darvill, Professor of Archeology in the School of Conservation Sciences at Bournemouth University. He's leading the first archaeological excavation at Stonehenge since 1964.

You can follow the Stonehenge dig

Interactive 360° panoramic of Stonehenge

Wainwright and Darvill standing in front of one of the smaller bluestones

Now for the answer to our quiz:

Some archaeologists believe that bluestone used to construct parts of the Stonehenge monument can be traced to a craggy rock outcrop in the Preseli Hills in the Welsh county of Pembrokeshire. The mountain site is named Carn Menyn.

Carn Menyn: http://www.flickr.com/photos/8725275@N03/