Construction of the South-Eastern Motorway, over the remains of Carrickmines Castle in south Dublin, will start early in the new year, according to Dún Laoghaire-Rathdown County Council.
However, conservationists campaigning for the preservation of the archaeological remains vowed yesterday to do "everything that is peacefully possible" to prevent the site being bulldozed.
Tomorrow marks the 100th day of their occupation of the castle.
Bad weather in recent weeks has delayed the last stages of the archaeological excavations, according to Mr Éamonn O'Hare of the council's transportation department.
However, it was expected that excavations would be completed by about Christmas, he said.
Once part of a stone-lined ditch has been removed and relocated as promised, the site would be handed over to the motorway contractors, Ascon, in the new year.
Carrickminders, the group campaigning to have the route of the motorway bent around the site, says it will be a "catastrophe" for the State's archaeological heritage if the current plans are not altered.
"We're not against the motorway and we're not insisting that the dig go on indefinitely, but we want it done properly, with due regard for the importance of this site. We won't allow ourselves to sit and watch should an attempt be made to destroy our heritage," said Mr Ruadhán MacEoin, the group's spokesman.
A number of legal and other challenges to the construction of the motorway are pending. An Bord Pleanála has responded to a complaint by an An Taisce member by demanding additional information on the alterations proposed as a compromise by the Minister for the Environment, Mr Brennan, in October.
Mr O'Hare said the council had written to the board "refuting" the claim that a revised Environmental Impact Statement was needed before the road could proceed.
The council is also finalising its submission to an EU inquiry on the issue, he added.
Thousands of historical artefacts have been uncovered during a two-year archaeological dig of the castle site, at a cost of over €6 million.
Medieval historians believe the site was built as a fortified outpost against Gaelic invaders, and was occupied between the 13th and 17th centuries.
Mr Brennan claims the adjustments he has made will result in about 60 per cent of the site being saved. However, the Carrickminders say over 80 per cent will be destroyed.
