Archaeology: Revealed: new henge built 5,000 years ago

A prehistoric site as old and as important as Stonehenge will be unveiled next week. Kim Sengupta describes the discovery of an archaeological `marvel' in the West of England.

It has been described as an archaeological sensation, one of the largest and most elaborate prehistoric ceremonial sites ever discovered in Britain, and it is expected to be named in the future as a World Heritage Site.

Scientists found the circle of timber and a ditch, known as henge, in the summer at a site about 70 miles West of Stonehenge. It had been built at the end of the neolithic and beginning of the bronze age, between 3,200 and 2,500BC.

The site will be unveiled on Monday by English Heritage which says it is "at least as old and of comparable significance to Stonehenge which is unique in the world". However, for the time being the circle, measuring 135 metres in diameter, will be left unexcavated.

A team under Dr Geoffrey Wainwright, chief archaeologist of English Heritage, found the hidden site under a field during a geophysical survey. The study had been carried our because examples of other ancient remains had been located in the area.

Using magnetometry, in which machines are used to test and locate material underground without the danger of damage which can be caused by digging, the team uncovered the equivalent of an underground version of Stonehenge.

The site may have been used for burials, with specific areas designated for burial rites. It could also have been used at some stage as a place of worship. The structures are believed to be geometrically positioned, part of it in the shape of a horseshoe.

Stonehenge rises above the ground because parts of it had been dug up. But English Heritage have no plans to do the same to the new discovery. One English Heritage specialist said: "We no longer dig everything up as a matter of course, but something will be organised to show visitors just what lies below the ground."

Parts of the structure, it is believed, may have been constructed elsewhere and transported to the location. It is also likely there were several stages of building spanning a number of years.

Like Stonehenge the building work may have been designed to mark the midsummer sun rising, and periods of the moon, although the archaeologists have been careful not to make any specific pronouncements about this or any involvement of druid priests.

It is likely the discovery will become a place of pilgrimage for those following alternative lifestyles, and believers of earth powers, say officials at English Heritage. Sir Jocelyn Stevens, chairman of English Heritage, has taken a keen interest in the project. He will be present on Monday for the unveiling along with Dr Wainwright, and Dr Andrew David, the organisation's head of archaeometry.