Scientists set out to unlock secrets of Stonehenge

By Jeremy Lovell

STONEHENGE (Reuters) - Archaeologists set out on Monday to unlock one of the secrets of Stonehenge, the majestic monument in southern England -- when were the first standing stones placed at the ancient religious site?

The concentric stone circles that make up Stonehenge, 80 miles (130 km) southwest of London on the sweep of Salisbury Plain, consist of giant sandstone blocks or sarsens and smaller bluestones -- volcanic rock of a blueish tint with white flecks.

Stonehenge experts Tim Darvill and Geoff Wainwright will use modern carbon dating techniques and analysis of soil pollen and sea shells to work out when the stones were set up, in the first archaeological dig at the World Heritage site since 1964.

"If you want to find out why Stonehenge was built, you need to look 250 kilometres away to the Presili Hills in north Pembrokeshire, where the first bluestones that built Stonehenge come from," Wainwright told reporters as the two-week dig began.

The two archaeologists, who have worked extensively in the Presili Hills in recent years, believe the bluestones, which made up the first stone circles at Stonehenge, were thought to have magical curative powers.

The massive standing stones, set up as long as 5,000 years ago, dominate the even older religious site, marked by numerous burial mounds or barrows.

"If you want to find out when the first stone was placed at Stonehenge, you need to dig a small trench round one of the stone's sockets and date what you find. That is what we are doing," Wainwright said.

Theories of the role of Stonehenge range from the supernatural -- one says the legendary wizard Merlin built it -- to sacrifices linked to sun worship.