A boulder chamber discovered by a hillwalker on a mountainside in Mayo was a ritual site for the dead, experts have revealed.

The remains of at least 10 adults, adolescents and children were placed in the cave-like structure over the course of 1,200 years in the Neolithic era.

Scientific analysis of adult bones found in the chamber dates them to 3,600 BC, while a bone of a child skeleton dated to 2,400 BC.

The discovery was made in August 2016 by local hillwalker Michael Chambers, who came across the chamber among massive boulders on Bengorm Mountain in the Nephin Beg range.

It is believed the chamber was not a burial site but used as a ritual place for bodies to decompose before bones were removed.

Mr Chambers found ancient human bones scattered over the rock floor.

Large pieces of quartz rock had been placed in and around them.

Marion Dowd of IT Sligo was called in by the National Monuments Service of the Department of Culture, Heritage and the Gaeltacht and the National Museum of Ireland to carry out a rescue excavation.

“When the radiocarbon dates came through it was very exciting. Not only were the bones Neolithic, but the dates showed the site had been used for over 1,000 years,” Dr Dowd said.

The research suggests bodies were taken into the cave chamber and laid out in a pit, and at some later point the skulls might have been deliberately broken as part of a complex burial ritual and larger bones removed.

Osteoarchaeologist Linda Lynch, who examined the bones, said: “This was not a burial site as such, but a ritual place where bodies were placed to decompose.

“Only a very small proportion of each skeleton was found, with the majority of bones apparently deliberately removed. The discovery indicates highly complex processing of the dead.”

Josepha Madigan, Minister for Culture, Heritage and the Gaeltacht, said: “This is a fascinating archaeological discovery and I want to thank the community of hillwalkers for reporting it to us.

“Such vigilance is extremely important to us in helping to protect and understand our archaeological heritage.

“The excavation has provided a glimpse into prehistoric Ireland over 5,000 years ago.

“Such discoveries show the enduring capacity of archaeology to enthral and demonstrate how advances in scientific research are affording us a better understanding of Ireland’s ancient past and its people.”