The European Commission has written to the Department of Transport seeking clarification of the route selection process, which led to the design of the South Eastern Motorway in south Co Dublin.
The Commission was reacting to complaints by An Taisce and other conservationists that the process was flawed.
The European Commission's Directorate-General for Environment has asked the Irish authorities to comment on a wide range of claims that the amount of knowledge which was available to the planners was deficient - particularly with "regard to the archaeological impact of the motorway project".
It has also asked how the scheme can be said to have considered and taken on board a 1983 An Foras Forbatha archaeological report on an earlier road scheme, which warned of the presence of the ruins of Carrickmines Castle in the area.
It has also sought information on:
"Expert submissions by archaeologists or historians, in particular by Dúchas."
"The impact of the motorway project on the Carrickmines complex, including expert comments by Dúchas and the National Museum of Ireland."
"The aspects of unexcavated remains and extent of proposed destruction of the site."
"Why it is not considered possible to undertake a more complex excavation and/or more extensive site preservation."
