The revised construction plan for the M50 motorway is "a huge gamble" that may cost taxpayers dearly, campaigners for the protection of Carrickmines Castle have claimed.
It has emerged Dun Laoghaire Rathdown County Council has negotiated a new contract with construction group Ascon that will allow the building to continue without completing the controversial section of the road.
However, the council has also expressed hope that the Carrickmines section will be completed once legal and environmental challenges are resolved.
The Carrickmines Castle Preservation Group (CCPG) said that if it is decided in the High Court that Carrickmines Castle is a national monument, further construction of the M50 under the current plan would not be possible.
Spokesman Vincent Salafia said: "We have never been against the motorway itself, and in fact have put forward a comprehensive plan that realistically allows for completion of the motorway, without any variables.
"The DLRCC action is open-ended, and has the potentialto delay final completion by years, costing millionsof euros," Mr Salafia claimed.
Meanwhile, the country's largest motoring organisation said the completion of the M50 was "an economic imperative". The AA said the motorway must be finished for the sake of the economy and for the benefit of the congested suburbs of south Dublin.
AA Ireland's public affairs manager, Mr Conor Faughnan, said: "From the city's point of view, the M50 has had such a long and chequered history that from a planning point of view it has become a fiasco more or less from start to finish," he said.
The significance of the Carrickmines site was not realised until the dig began in 2000. Archaeologists found a well-preserved castle wall surrounding buildings, workshops, houses, kilns and wells. Up to 20,000 pieces of medieval pottery as well as coins, cannon balls, weapons, skeletons and textiles were also recovered.