In 1642 Carrickmines was the scene of a battle when the castle, occupied by rebel Irish forces, was sacked and overrun by Crown forces who massacred the 300 men, women and children inside.
An outpost of the Pale - a fortification to protect Dublin and its surrounding areas from the hostile native Irish raiding the loyal garrisoned area - the Castle was destroyed, the only visible remnant being part of a gatehouse which remains today.
The site was of immense archaeological significance, says the project archaeologist Valerie Keeley and the road presented a unique opportunity to study it. 'It is the first Pale castle ever to be excavated, and it has been a really positive and productive excavation, ' she says.
'We have a huge amount of metal finds, weapons, ceramics and imported materials and textiles from France, for example. A lot of material has been gathered for our national heritage, ' she says. A detailed report will be produced when studies of what has been found are complete. Artefacts will be placed in Ireland's National Museum.
But she regrets the dispute.
'The archaeological work was being carried out entirely in accordance with the environmental impact statement and the correct and agreed procedures. The dispute was due to a small group of agitators.'
'This damages archaeology, which some people see as something which holds up road projects. Events might have turned out differently particularly if the public knew how much archaeology had been done at the site.'
Sections of castle and ditch are being removed piece by piece, with their precise original locations logged.
Huge quantities of site material are being sieved - work which does not pose any delay to road building - to ensure everything of archaeological relevance is found.