GARDAI are hunting vandals who attacked a 5,500-year-old standing stone at the Hill of Tara in Co Meath with a hammer.
Damage has been caused in 11 places on all four faces of the Lia Fail Standing Stone -- also know as the 'Stone of Destiny' -- which is mentioned in ancient texts about the High Kings of Ireland.
Minister for Arts and Heritage Jimmy Deenihan last night said his department was examining the possibility of increasing surveillance at such monuments.
An archaeologist from the National Monuments Service carried out a detailed examination of the monument after the Office of Public Works (OPW) discovered the damage at the weekend.
Archaeologist Tom Condit said the damage was visible on the stone's surface but a search of the area did not reveal any of the fragments, which may indicate that they were taken away.
Mr Condit said such "obviously wanton" damage was rare.
"It is disturbing that someone would select a site as well known and as vulnerable as that," he said.
But Mr Condit warned that "short of closing sites off" it was difficult to protect them.
He urged anyone with information to inform the gardai.
Under the National Monuments acts, anyone convicted of interfering with a national monument can face a fine of up to €10m or five years' imprisonment.
Dr Conor Newman, chairman of the Heritage Council, said: "So many of our items are out in the open and it is a terrible breach of the trust that we rely on to protect and guard such monuments. It wouldn't be the right thing or possible to police all monuments. We rely on trust, public vigilance.''