Stonehenge is easily the most famous stone monument in the world. Now, just two miles away, archaeologists have discovered the remains of another massive monument that has been hidden just under the Earth’s surface for thousands of years. Researchers used radar mapping to determine the monument consists of at least 90 stones – 30 of which appear to be intact – that measure up to 4.5 meters (15 feet) tall. The stones are arranged in a giant C bordering a dry valley and facing toward the river Avon.

Researchers are calling it “archaeology on steroids.” Vince Gaffney is an archaeologist at Bradford University and he leads the Stonehenge Hidden Landscape project. “What we are starting to see is the largest surviving stone monument, preserved underneath a bank, that has ever been discovered in Britain and possibly in Europe,” he said. They believe the stones were put into place some 4,500 years ago, but as with Stonehenge, researchers are not entirely sure why.

Related: Digital mapping of Stonehenge reveals site is more massive than we thought

The stone formation, which is now being called the Durrington Walls stones, is presumed to be a ritual arena of some sort, according to Gaffney. Because most of the stones are damaged and were revealed by the radar scan to be lying down, archaeologists have to speculate about what the structure looked like when it was originally built. They believe the stones were standing, just like those at Stonehenge, and that they were likely knocked over by Neolithic builders once the site was no longer needed for its intended purpose.

The one-mile circumference of Durrington Walls makes it one of the largest known henge monuments on the planet. It’s also surrounded by a ditch and a 40-meter (131-foot) wide, 1-meter (3.3-foot) tall outer bank which were both presumably constructed by man as well.

Via The Guardian

Images via Ludwig Boltzmann Institute