The National Roads Authority (NRA) has denied the meandering route of the M3 motorway from Clonee to Kells had been designed to avoid cutting through big farms in Co Meath.
Brian Swan, who farms next to the Hill of Skryne, claimed that it "meanders like a rattlesnake" to suit the county's big farming interests.
"If the NRA could move it for them, they could easily move it to protect our heritage," he said.
An NRA spokesman said it was "unfair and inaccurate" to suggest that large landowners had been specifically facilitated by the route-selection process for the M3, though minimising farm severance was one of the considerations.
"The logical line of the route would have been to the west of Tara, but we didn't do that in order to mitigate its visual and archaeological impacts.
"The loop we're taking now is longer and is affecting more land as a consequence."
An outspoken opponent of the motorway, Mr Swan conceded that it did not affect his 200-acre farm.
"But I'd say every farmer along the route is afraid to speak out because they know if they open their mouths they'll lose out."
The NRA confirmed that farmers affected by the motorway would receive "co-operation money" amounting to an extra €5,000 an acre for allowing access to their land - roughly 15 per cent more than its acquisition cost.
Michael Egan, director of corporate affairs, said there was nothing unusual about this arrangement. It was in line with an agreement reached in 2001 between the Department of the Environment and the Irish Farmers' Association.
"Farmers had been refusing us access to their land and this was having a serious impact on the roads programme, so the agreement provided for these goodwill payments. The case of the M3 is no different," he said.
Mr Swan, whose family has been farming in Skryne for seven generations, said he was well aware of its history. "Every morning I get up I'm reminded that this place has been affected by every period of history. I don't think it belongs to us to plunder.
"It's a sacred place that belongs to our ancestors, and we shouldn't be touching it. The old road between Skryne and Tara is still there, marked by a double-ditch, and when I show that to people, especially foreign visitors, they go silent in wonder."
Tourists "can't believe that a motorway is planned to run through this valley. I thought it couldn't happen either, so I was late getting involved in the campaign. But I'm going to do whatever is required of me now to help stop it."
Raymond Manley, a Dundalk-based engineer, said all interested parties should meet in a non-confrontational atmosphere to devise the best solution and "avoid mistakes before they happen".
On a recent visit to Stonehenge he noted plans to remove one of the two roads which run close to this World Heritage Site and to put the other one underground so Stonehenge could be viewed in a grassland setting.
The current car-park would be grassed over, and a new visitor centre built some 3km away, according to English Heritage, the National Trust and the Highways Agency.
"Having visited Tara a number of times, it struck me that we should be learning from the Stonehenge experience of past mistakes before we make similar ones ourselves and be faced with a costly process of trying to fix it at some later time," Mr Manley said.