I'm convinced it's "Construction of the Third Kind"...

During the 20th century, excavations at Stonehenge revealed that the structure was built in stages and that it dates back some 5,000 years,to the late Stone Age. The meaning of the monument, however, was anyone's guess -- until recently. Who built Stonehenge? What was its purpose? How did prehistoric people quarry, transport, sculpt and erect the giant stones? A new generation of researchers is tackling these questions, finding important clues in the landscape surrounding Stonehenge --prehistoric structures we can actually touch...NOVA 8pm