The mysteries of Stonehenge are revealed sometimes by unusual methods—forgetting to water its grass or whacking its stones with quartz. In this case, it just took four years of staring at the ground. A new underground survey reveals a vast complex of unknown Neolithic monuments near Stonehenge, including a huge stone "super henge."

The Stonehenge Hidden Landscape Project has spent the past four years sweeping the area around Stonehenge with ground-penetrating radar and GPS-guided magnetometers. Without ever picking up a shovel, archeologists have mapped the ground up to two miles deep in extraordinary detail. It's staring at the ground—but with high-tech tools.

Surveying the ground around Stonehenge. Credit: Stonehenge Hidden Landscapes Project

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Among the hundreds of features that were mapped are 17 newly discovered Neolithic monuments, all dating to the same period as Stonehenge about 5,000 years ago. These pits and ditches, marked by post holes, often seem to be astronomically important.

There is the Cursus, for instance, a rectangular space which is under two miles long and 300 feet wide. Two pits inside the Cursus appears to be aligned with the rising and setting sun on the summer solstice when seen from the Stonehenge's heel stone. Taken together, the monuments suggest Stonehenge is the most obvious remainder of a large complex of structures with ritual importance.

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The survey also revealed surprising facts about known structures, like the Durrington Walls, a dirt bank that encircles a circumference of a mile. Underneath one section of the dirt, archeologists found more than 50 huge stones, each 10 feet long, forming a "super henge." "That's a big prehistoric monument which we never knew anything about," the co-director of the investigation, Professor Vince Gaffney, told Nature. The structure, which faces the River Avon, could have a ritual connection with the water.

The BBC is a devoting a two-part TV series to the Stonehenge Hidden Landscape Project, which will air on the Smithsonian Channel in the U.S. beginning September 21. For the more immediately curious, Smithsonian Magazine also visited the scene of the survey, where tractors pushed ground-penetrating radars "like high-powered lawn mowers" and all-terrain vehicles "dragged the magnetometer sensors on long strings." This is what modern archeology looks like: no shovels, lots of gizmos, and big data. [Financial Times, The Independent, Nature]

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