Drunken revellers pulled stones from An Grianan Fort in Co Donegal, defecated in a holy well, and then abused tourists.
The incident happened over the weekend when a group of people came at the site for a party.
Two of the men who took part in the incident appeared at Letterkenny District Court yesterday.
William Sweeney, aged 19, and Raymond McCormick, aged 21, appeared in court charged with causing criminal damage to the fort on Jul 6.
Garda Eddie Doherty described the scene which met him when he went to investigate complaints.
He said he found women’s underwear, human excrement, beer bottles, and historic stones thrown around the fort. He added that tourists were left stunned by the scene.
“It was just a scene of carnage. The tourists who were visiting the area were traumatised by what they saw,” said Garda Doherty.
Judge Paul Kelly said he was shocked by the “ignorant, loutish and thuggish’ behaviour. : “This monument is one of the best preserved of its kind and I visited it myself some months ago... It has stood the test of time by many invading armies over the years and then this group of thugs come along and invade it and start to dismantle it from the inside.”
The solicitor for McCormick, of 8 Ballbane Pass, Creggan, Derry, and Sweeney, of 4 Oaklands Park, Creggan, Derry, said both men were embarrassed by what had happened.
He said they were only charged with criminal damage and were not involved in any defecating incident.
They had pleaded guilty to throwing historic stones and empty cans of beer.
He said both men had been in custody since the incident.
The court was told the Office of Public Works is examining the extent of the damage to the site.
Judge Kelly remanded both men in custody until Thursday at Buncrana Court and said he wanted to hear from the OPW how much monetary damage had been done to the area.