An astonishing complex of ancient monuments, buildings, and barrows has lain hidden and unsuspected beneath the Stonehenge area for thousands of years. Scientists discovered the site using sophisticated techniques to see underground, announcing the finds this week.

Among the discoveries announced Wednesday are 17 ritual monuments, including the remains of a massive "house of the dead," hundreds of burial mounds, and evidence of a possible processional route around Stonehenge itself.

There's also evidence of a nearby mile-long "superhenge" at Durrington Walls that was once flanked by as many as 60 gigantic stone or timber columns, some of which may still lie under the soil.

The discoveries result from the Stonehenge Hidden Landscape Project, a four-year effort to create a high-resolution, 3-D underground map of the landscape surrounding Stonehenge.

The project team, led by researchers from the U.K.'s University of Birmingham and Austria's Ludwig Boltzmann Institute, mapped the area down to a depth of about ten feet (three meters) using ground-penetrating radar, high-resolution magnetometers, and other state-of-the-art remote-sensing equipment.

In all, nearly 3,000 acres have been excavated virtually, making this the largest and most ambitious project of its kind ever undertaken anywhere in the world.

"Nobody had any idea this was here," says lead scientist Vince Gaffney, professor of landscape archaeology at the University of Birmingham. "Instead of a monument in isolation, we find that Stonehenge was part of a rich monumental landscape."

Profound Find

Many of the 17 newly discovered monuments appear to be shrine-like structures. The small circular constructions, contemporaneous with Stonehenge's busiest period, are placed around the main stone ring and form a sort of Neolithic analogue to the Via Dolorosa, held to be the path Jesus walked to crucifixion, Gaffney suggests.

"What we could be witnessing here is the birth of the idea of ceremonial procession, or a liturgy," he says.

For centuries, the enigmatic stone circle, built over 4,000 years ago on England's Salisbury Plain, has awed and intrigued visitors. (See "Stonehenge Revealed: Why Stones Were a Special Place.")

"Stonehenge is where archaeology got its start," says Nicola Snashall, an archaeologist from England's National Trust, which looks after the monument.

"Antiquarians like John Aubrey and Inigo Jones began digging here in the 17th century to try to unlock its secrets—some of the world's very first archaeological excavations."

With no written records to fall back on, the mysterious stone structure has spawned countless theories involving Celts, Druids, Romans, and even the King Arthur legend. Its original shape has been a matter of great debate, including whether it was built as a semicircle, as seen today, or a full circle of stones.

This past summer, a chance dry spell revealed patches in the soil that marked where stones once stood. But nobody suspected the incredible wealth of ruins that lay hidden beneath the soil.

Deep Views

High-tech remote sensing and underground mapping is changing not only what is known about Stonehenge, but also the way archaeology is done.

In Orkney, a group of islands in northern Scotland, such a survey revealed a vast, sophisticated and entirely unsuspected Neolithic temple complex that predates Stonehenge by over 500 years. Archaeologists suggest the site may even have influenced the building of Stonehenge. (Read "Before Stonehenge" in National Geographic magazine.)

"Technology is opening doors for archaeology we could only dream about 15 years ago," says Gaffney, who compared the Stonehenge Hidden Landscape Project with a 3-D underground mapping project he undertook at the ancient British-Roman settlement of Wroxeter in the late 1990s.

"Back then, it took us four years to map 78 hectares, with about 2.5 million data points," he recalls. "With this latest survey at Stonehenge, we were doing that much in a week, [finding] new types of monument that had never been seen by archaeologists.