Gardaí in Co Meath are investigating vandalism to the Lia Fáil – the standing stone at the top of the Hill of Tara.
A spokesman for the Gardai confirmed that green and red paint was poured over the stone monument overnight.
It is believed that 50% of the 5,000-year-old granite is covered by the paint.
Not for the first time the monument has been vandalised. In 2012 the stone was damaged when pieces of it were hacked off with an ax.
Jimmy Deenihan the Minister for Arts, Heritage and the Gaeltacht has described this latest incident of vandalism as “truly shameful”.
Head of the conservation with heritage Council Ian Doyle has said “This is an act of cultural vandalism,” Mr Doyle also said that local people and others “have a close relationship with the Hill of Tara and this is an assault on their sense of pride and the respect, love and affection they have for it.”
Gardaí are appealing for anyone with information to contact the Garda Confidential Line on 1800 666111.