Work on the controversial M3 motorway in County Meath near Tara has been halted after the discovery of a highly significant archaeological find.
The road will be close to the ancient monument
The project has been bitterly opposed by environmental campaigners.
They are opposed to the route because of its proximity to the historic sites of Tara and Skryne.
The find is thought to be the size of several football fields and is a circular structure used possibly for ceremonies in ancient times.
On Monday, Irish Transport Minister Martin Cullen turned the first sod on the huge motorway project.
However, only one day later it has been halted by Environment Minister Dick Roche
Environmentalists and historians warned that the Hill of Tara and its ancient burial site in County Meath was too important to be tampered with.
The M3 is set to be built near the existing Enniskillen to Dublin road, which can be gridlocked at peak times.
The National Roads Authority had argued that the motorway was needed because it can currently take up to two hours to travel the 25 miles between Navan and Dublin.
However, some historians objected to its route past an area which they view as a treasure trove of archaeological finds and Ireland's equivalent of the Egyptian Valley of the Dead.
Tara, known as Temair, was once the ancient seat of power in Ireland - 142 kings are said to have reigned there in prehistoric and historic times.
In ancient Irish religion and mythology Temair was the sacred place of dwelling for the gods, and was the entrance to the otherworld.