Minister for the Environment Dick Roche yesterday sanctioned 38 archaeological digs in the Tara-Skryne valley in Co Meath, effectively approving the proposed M3 motorway.
However, Mr Roche has blocked the route of the proposed N25 bypass of Waterford city by issuing a requirement for the protection in situ of a recently discovered Viking settlement at Woodstown.
The Minister said he saw no conflict between the decisions, as it was possible to realign a very short section of the N25 to protect the Woodstown site.
On the M3, where the 38 sites had been discovered on a 15.5km stretch of the proposed motorway between Dunshaughlin and Navan, such variations would not be possible without substantially rerouting the motorway, he indicated.
However, the decision on the M3 is expected to be challenged almost immediately in the High Court by groups campaigning against the route.
Speaking at a press conference in Government Buildings yesterday, Mr Roche reiterated his view that the route of the M3 motorway had been decided by An Bord Pleanála in 2003.
His own role was limited to how best the archaeological works should be handled, he maintained.
The 38 sites, some of which are within a few kilometres of the Hill of Tara, will now be subject to rigorous investigation and resolution, the Minister said.
But he refused to be drawn on a timeframe for the construction of the road, saying the excavations required would be "onerous", costing at least €30 million to €40 million and more if required.
It is expected the excavations could last about two years, with construction taking at least another three. While it was essentially a matter for the National Roads Authority (NRA), the Minister ruled out building the 59km motorway from Clonee to north of Kells in phases.
Mr Roche said that once constructed, a "robust planning control regime" would be put in place to prevent "inappropriate development" in the vicinity of the Hill of Tara. He also revealed that the NRA had agreed to a revised design of the proposed Blundelstown interchange close to the Hill of Tara.
The revision omits lighting columns to lessen the visual impact of the junction on the hill, while including a landscaping and tree-planting scheme.
Describing the conditions for the excavations as stringent and his own approach as punctilious, Mr Roche said he was satisfied the directions he was issuing would ensure best practice in preserving archaeological sites by record, and that the process would add greatly to our knowledge of past history.
Mr Roche acknowledged opposition to his decision from the director of the National Museum, Dr Pat Wallace, from whom he had received a statutory report. Dr Wallace's concerns were reflected in the directions made, he said.
But Mr Roche said he was surprised a "chorus" of Irish and international academics opposed to the road had made their opinions known only after the statutory planning process held by An Bord Pleanála.
Among the conditions imposed are that: all archaeological works should be undertaken by professional archaeologists in advance of road construction; all work must be subject to inspection by State archaeologists with regular progress reports; artefacts uncovered be sent to the National Museum; additional time and/or money must be made available to ensure proper resolution of the sites if necessary.
Mr Roche said he hoped the archaeological work could begin immediately.
