The Stoneyfield kerb cairn was saved from destruction and moved by volunteers to a site next to Raigmore Hospital in Inverness in the mid-1970s as the road was expanded.
Research shows the stones were part of a bigger monument that included a timber building, a stone hearth and a series of cists used for cremations.
Analysis has also shown that explosives were used to blast apart some of the stones at one time.
Now, vandalism has been added to its long and complex history after one of the larger stones was damaged when a plaque telling the story of the cairn was ripped off.
Keith Fernie from Inverness spotted the damage when he was cycling to work.
Mr Fernie told the Press and Journal: “It’s really quite sad when people do that, considering all the work that went into shifting it and all the volunteers; it’s very sad to see it being abused.
“Amazingly this 5000 year old monument was painstakingly shifted stone by stone to its present location by a group of volunteers without whose efforts the ring would have been bulldozed in the construction of the new A9.
“The community at Raigmore do wonders in looking after it, keeping it in a good state of repair so it’s very disappointing for them to see it being tarnished in that way.
“This is not really the way to remember the volunteers. What way was this to repay such public-spiritedness, and who wouldn’t despair of such mindless vandalism?”
The plaque was put in place 2013 as part of a project to regenerate the area .
Director of Archaeology Scotland, Eila MacQueen added: “This site was one of the projects we worked on a few years ago after it suffered from a lack of recognition in terms of their being a bit of anti-social behaviour going on around it.
“It’s disappointing to see and hear there has been some vandalism to it as the site means something to the people of Inverness.”
A Highland Council spokeswoman added: “The cairn has had a long and complex history and has been saved more than once by the strength of local support to ensure its survival and its place at the heart of the Raigmore community.”