The Trefael Stone in Pembrokeshire was thought to be just one of many linked to nearby Bronze Age locations.
But it has now been reclassified after a survey established it as the capstone of a Stone Age ritual burial chamber.
The survey revealed the location, near Nevern, has been used for ritual burials for at least 5,500 years.
An archaeological team from the University of Bristol has been given permission to examine the human bones found there along with beads and shards of pottery.
Story: Nick Dermody, BBC Wales News | Photo: BBC News