Archaeology expert Conor Newman, appointed by Minister for the Environment John Gormley to advise on the excavation of the national monument at Tara, has said he will continue to campaign against the routing of the M3 through the area.
Meanwhile, the National Roads Authority said it will employ 24-hour security at the Lismullin site, after accusing conservationists of "trespassing, being a health and safety risk and damaging archaeology".
Mr Newman, a lecturer in archaeology in NUI Galway, said his acceptance of the advisory role should not be seen as an endorsement of the motorway plans which were an "alarming, depressing, disastrous mistake".
Mr Newman was appointed this week to a special committee to advise on the excavation of the Lismullin site, which was uncovered during preparatory work for the M3.
"I am fundamentally opposed to this road," he said yesterday. "I remain fundamentally opposed to it and whatever advice I give should not be seen in any way as absolution for this motorway going through."
Mr Newman, who is one of the foremost archaeological experts on the Hill of Tara and who made submissions against the motor- way route to An Bord Pleanála, said it was not too late for it to be rerouted. "Obviously money has been spent, but not so much as to make it necessary to compound the mistake made in choosing this site for the road by continuing to construction."
However, the NRA accused conservationists of "claiming they have made discoveries and that they are protecting the archaeology, when the reverse is the case". Michael Egan, a spokesman, said some conservationists claimed the discovery of a souterrain in recent days and described it as "new". But he insisted it had in fact been officially notified to the Department of Environment on April 18th last.