A long barrow from Britain's Stone Age has been discovered in Wiltshire, close to the famous Stonehenge monument in Avebury. The burial mound dates from about 3,600 BCE, several hundred years before Stonehenge was built.

Found in an agricultural field at a site called Cat's Brain in the Pewsey Vale, the monument consists of a central rectangular building surrounded by two long, curved ditches on either side. It lies halfway between the monuments of Stonehenge and Avebury.

The mound has long since been eroded by regular ploughing, but the archaeologists – made up of staff and students from the University of Reading's Archaeology Field School – say that the deeper parts have been preserved. The researchers have now begun to search for human bones that may still remain intact.

"This incredible discovery of one of the UK's first monuments offers a rare glimpse into this important period in history. We are setting foot inside a significant building that has lain forgotten and hidden for thousands of years," said Amanda Clarke, co-director of the field school.

As well as human bones, the team hopes to discover artefacts and other environmental evidence that can reveal clues about how these ancient people lived.

Despite being in an area of rich archaeological significance for the UK, the discovery is a rare one. It is the first ancient burial mound to be excavated in Wiltshire for 50 years.

"Opportunities to fully investigate long barrows are virtually unknown in recent times, and this represents a fantastic chance to carefully excavate one using the very latest techniques and technology," said Jim Leary, also co-director of the field school.

House of the Dead
The 'House of the Dead' viewed from the air. University of Reading / Andy Burns

"Discovering the buried remains of what could be the ancestors of those who lived around Stonehenge would be the cherry on the cake of an amazing project."

The field school is holding an open day on Saturday 15 July at nearby Marden henge, where members of the public will be able to see the archaeologists in action.