There have been clashes at the construction site in the Tara valley where the Dublin government is attempting to construct a motorway through an important archaeological site.
A giant iron-age henge found in the path of the motorway may be a significant ceremonial site for the ancient capital, one of the most important unexplored archaeoological sites in western Europe.
Conservations with the Campaign to Save Tara have attempted to block access to and from a compound where plant and machinery are stored by contractor Siac Ferrovial.
They were aided by a small group who attempted to block entrances to the construction site about 1km north of Dunshaughlin in County Meath.
But 72 hours of peaceful protest ended in violence when construction workers assaulted the protestors.
One activist who asked not to be identified said he had been kicked while another female member of the group had been thrown into a ditch.
The protesters had refused to move to allow the lorries and plant to leave the compound.
The spokesman said, however, that bulldozers were used to create new entrances, a move he insisted was in defiance of planning permission.
A group of conservationists had their names were being taken by a team of eight gardai who said they were trespassing on private property.
However, the protest continued at the weekend following the discovery of further significant underground archeological remains.
Members of the Campaign to Save Tara and the Tara Solidarity Vigil said the man-made structure, which appears to be about nine metres long, was revealed when construction workers were using heavy machinery for stripping topsoil last Saturday.
Ancient gravestones were dumped in piles of topsoil and bones were visible in excavated spoil from the route of the motorway.
Dr Muireann Ni Bhrolchain, of the department of medieval Irish studies at NUI Maynooth, said the conservationists would occupy the site until staff from the National Museum of Ireland arrived to assess the find. Its discovery highlighted the “inadequacy of the preliminary investigations” on the route, she said.
“Perhaps this discovery explains why construction workers were so heavy-handed with the conservationists. . . Did the NRA [ National Roads Authority] and the contractors realise that there was something to hide here?”, Dr Ni Bhrolchain said.