Stonehenge is the gift that keeps on giving -- the gifts being expansive, mysterious arrangements of massive stones.

Researchers in England recently found another monument at Stonehenge, just two miles from the original stone circle. Scientists say it may be the largest collection of stones at the site, and unlike anything else in the world.

The ancient monument was discovered buried beneath a grassy ridge at the southern edge of Durrington Walls, a sizable Neolithic settlement near Wiltshire, England. None of the stones have yet been unearthed, but were studied using ground-penetrating radar.

The monument consists of a 90 monoliths arranged in an arena-like C-shape. Some of the stones are 15 feet tall. Researchers say the so-called superhenge was arranged some 4,500 years ago.

Many of the stones appear to be purposefully pushed onto their sides. While many of the monoliths are now fragments, 30 of the buried stones remain entirely intact. The stones originally encompassed a ringed ditch and earthen mound.

"It's truly remarkable," Vince Gaffney, lead archeologist on the Stonehenge Hidden Landscapes Project, said in a statement. "We don't think there's anything quite like this anywhere else in the world. This is completely new and the scale is extraordinary."

There is no direct evidence of what inspired the monument's design, but experts say the arrangement may be related to the changing seasons, with a row of the smaller stones aligned with rising sun at its lowest arc during the winter solstice. The arena's axis also aligns with the midsummer sunrise.

In addition to being a calendar of sorts, the theatrical nature of its size and shape suggest the monument also served as a place of worship, ritual and socializing. It's possible large numbers of Neolithic settlers gathered at the site for celebrations.

"Not only does this new evidence demonstrate a completely unexpected phase of monumental architecture at one of the greatest ceremonial sites in prehistoric Europe, the new stone row could well be contemporary with the famous Stonehenge sarsen circle or even earlier," Gaffney said.

"This latest work has given us intriguing evidence for previously unknown features buried beneath the banks of the massive henge monument at Durrington Walls," added Phil McMahon, an archaeologist with the British preservation agency Historic England. "The possibility that these features are stones raises fascinating questions about the history and development of this monument, and its relationship to the hugely important Neolithic settlement contained within it."