Work is due to resume tomorrow morning on the final section of the M50 motorway, following a High Court ruling this afternoon.
Conservationists had taken a constitutional action to try to halt work on the site of the ruins of Carrickmines Castle in South County Dublin.
Objectors had argued that the final stretch of the M50, which runs over what is left of Carrickmines Castle, requires an additional environmental impact study under EU law.
They also challenged the constitutionality of two aspects of the amended National Monuments Bill. They argued that it gave the Minister for the Environment excessive powers, and that it did not uphold the constitutional right for the protection of the country's heritage.
But in a 69-page ruling, Miss Justice Mary Laffoy ruled against each of the three arguments. A decision on costs will be made in October.
The man who brought the action, Dominic Dunne, said he had no comment to make following the ruling. However, he did say that as far as he was concerned it was not over.
Mr Dunne’s legal team is now considering an appeal, and suggested that no work should be carried out on the disputed site until it had reached a decision.
However, Dun Laoghaire Rathdown County Council's Senior Engineer, John McDaid, says that work will resume in the morning.