A cross-border heritage group has been protesting against plans to build a rubbish incinerator near the site of the Battle of the Boyne in County Louth.
Neolithic burial mound Newgrange is a World Heritage Site
The demonstrators called on the Irish Government to stop what they described as "cultural vandalism".
Each year, Orangemen commemorate Protestant Prince William of Orange's 1690 Battle of the Boyne victory over Catholic King James II.
The site in the scenic Boyne Valley has been developed in recent years as a tourist attraction.
Speaking on Sunday, Brian Hanratty of the group, the Battle for the Boyne, said it would be "an appalling folly and an appalling act of cultural vandalism" if the scheme went ahead.
"We are protesting at plans to build a large municipal waste incinerator literally right on the footprint of the battle site and just minutes from Newgrange," he said.
A mural on a wall in Belfast depicting the Battle of the Boyne
The protest was timed to coincide with the winter solstice which is marked at Newgrange, a neolithic burial mound in County Meath.
People traditionally gather on the shortest day of the year to watch light from the sun enter a chamber at the World Heritage Site.
Mr Hanratty said that World Heritage status should be extended to include the battle site.
World Heritage status is granted by Unesco, which is part of the United Nations.