A “House of the Dead” dating back more than 5,000 years could contain the remains of the ancestors of people who lived around Stonehenge, archaeologists have said.

A Neolithic long barrow burial mound in a place known as Cat’s Brain, in Pewsey Vale, Wiltshire, is being excavated by University of Reading experts and students in the first full investigation of such a monument in the county for half a century.

The long barrow, found in the middle of a farmer’s field halfway between the two major monuments of Avebury and Stonehenge, was first spotted by aerial photography and than assessed by geophysical survey imagery.

An aerial view of the site being excavated near StonehengeAn aerial view of the site being excavated near Stonehenge (PA Picture desk)

It consists of two ditches flanking what appears to be a central building, which may have been covered with a mound made of the earth dug from the ditches, but has been ploughed flat over the centuries.

Experts said it was surprising to find lasting evidence of the building and believe it may contain human remains buried there in around 3,600 BC.

It is hoped the investigation will provide crucial evidence from the early Neolithic period, which saw Britain’s first agricultural communities and monument builders.

Members of the public can attend an open day on Saturday to see the excavation happening live as the team searches for human remains, artefacts and other environmental evidence for further analysis.

Dr Jim Leary, director of the Archaeology Field School, said: “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.

“Members of the public now have the chance to visit us and see prehistory being unearthed as we search for human remains on the site.

“Discovering the buried remains of what could be the ancestors of those who built Stonehenge would be the cherry on the cake of an amazing project.”

Amanda Clarke, co-director of the Archaeology Field School, said: “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.”

In addition to the Cat’s Brain long barrow, the field school is working at Marden henge, built around 2,400 BC in the Vale of Pewsey, which is the largest henge in the country but has had little archaeological investigation.