The new henge, called Bluestonehenge because it was built with blue Preseli dolerite mined more than 150 miles away in Wales, was on the banks of the River Avon, where ancient pilgrims carrying the ashes of their dead relatives began the journey from the river to Stonehenge, nearly two miles away. Some are calling it the "little sister" of Stonehenge.
The approximately 25 massive bluestones were erected in a circle about 5,000 years ago, and eventually were encircled by a ditch and an earthen embankment.
About 500 years later, however, the stones were moved and incorporated into Stonehenge itself.
All that is left of the circle are the holes where the stones sat in the ground and a few chips of dolerite.
The fact that the monument was found at the beginning of an avenue leading to Stonehenge and near the river "not only solidifies the view that Stonehenge covers the entire landscape, but also the sacred importance of the river itself," said archaeologist Christine Hastorf of UC Berkeley, who was not involved in the research.
"It means that there was a link between Stonehenge and the water, out to the ocean," she said.
Stonehenge is made up of concentric circles of massive stones, some weighing as much as 50 tons, surrounded by a ditch and an earthen bank. The structure is aligned with sunrise on the summer solstice, and researchers have long viewed it as both an astronomical observatory and a cemetery.
A team led by archaeologist Michael Parker Pearson of the University of Sheffield made the discovery while excavating in the area of Stonehenge during the last several years.
Its findings have suggested that the entire site, which stretched from the river to Stonehenge, was a religious complex where ancient peoples gathered at certain times of the year to celebrate life and bury their dead.
Some of their discoveries have also suggested that Stonehenge was a burial site for early kings.
The team had long suspected there was some kind of monument near the river at the beginning of the avenue leading to Stonehenge, but it had great difficulty finding it, Parker Pearson said in a telephone interview Monday.
"We tried every method we could to prospect for the circle -- radar, magnetic signals, electrical resistance in the Earth -- but we couldn't see anything there at all."
Only when they began digging in August and September did they find what they were looking for.
So far, they have found nine holes that they believe were part of a 30-foot-wide circle of about 25 standing stones.
The holes are too wide and shallow for them to have contained wooden posts.
The holes are also too small to have held sarsen stones, the larger limestone rocks that form part of Stonehenge and that were mined at Marlborough Downs 25 miles to the north.
But the dimensions correlate precisely with those of bluestones in the inner circle of Stonehenge.
The stone circle at Bluestonehenge was eventually replaced by a henge, a circular ditch nearly 74 feet across with an external bank.