The Green Party's environment spokesman, Mr Ciarán Cuffe, has called for a compromise in the controversy about the M50 motorway through Carrickmines Castle in south Dublin.
His appeal came as protesters camped on the site brace themselves for what they expect is an "imminent push" as a €10 million archaeological dig at the castle comes to an end.
Mr Cuffe said last night the National Roads Authority and Dún Laoghaire-Rathdown Council should change the junction layout at Carrickmines so that more of the castle remains are protected.
"At this stage, we are not asking for the route of the motorway to be changed," he said. "However, we do believe that minor changes can be made to the approach roads which will safeguard the setting of the castle complex."
Mr Cuffe said the link road adjacent to the castle should be moved northwards. The roundabout should be removed and the junction adjacent to the "Jackson Way" lands simplified, using a signal-controlled junction.
Mr Cuffe said that at the "eleventh hour" the council, the NRA and the Minister for Transport, Mr Brennan, should compromise in the interests of an important archaeological site.
The council's senior engineer in charge of the project, Mr Eamonn O'Hare, has said the "next stage" of the work on the site will involve the removal of a section of castle fosse - essentially a walled ditch - from the line of the motorway, for conservation elsewhere on the site.
However, the protesters have said they will oppose the removal of the fosse and solicitors' letters on their behalf have been sent to the county manager, Mr Derek Brady.
The "Carrickminders" said the letters were the first formal step in a process which would lead to an application to the High Court to halt the construction work.
The castle was blown up in 1642 after surviving for about 500 years as a fortification for the city of Dublin.