Saint Patrick landed on the Boyne Estuary at Inbher Colpa before making his way upstream to Slane, where popular accounts say that he lit the Paschal Fire in defiance of the King of Ireland. This great Easter Fire was ignited a few days after Spring Equinox, in the year 433AD. Millmount, the supposed burial place of the Milesian leader Amergin, is the main ancient site overlooking Inbher Colpa. From here, a few days after Spring (Vernal) Equinox, the sun sets directly over the Hill of Slane, the place where Patrick lit the Easter Fire. Of course, Easter falls at the time of full moon following the Vernal Equinox. It is likely there is significant astronomy associated with Patrick's story. Slane is targeted from the east by an alignment after equinox with Millmount. It is also targeted from the west by the chamber of Cairn T at Loughcrew.
In our book, Island of the Setting Sun, we describe Patrick's Journey from Inbher Colpa to Slane as his "equinox journey". It is tied in with Neolithic cosmology. In the Neolithic, the sun at Spring Equinox was above the giant man figure of Orion - the huge light bearer of the sky. At autumn equinox, the sun was housed in Ophiuchus, the serpent bearer. Looking in the direction of Slane at the time of Autumn Equinox in the Neolithic, one would have been looking towards another giant man of the sky, Ophiuchus, grappling with the snake.
Recently, we've discovered just how astonishing the architects of ancient alignment were. Using Google Earth, we found that extending the line from Millmount to Slane westwards travels all the way to Croagh Patrick, perfectly intersecting the little chapel on the summit of the reek with breathtaking accuracy. Significantly, this line skirts the hills of Loughcrew on its way, and also travels directly through Cruachan Aí, one of the largest archaeological complexes in the whole world, with 200 monuments located in a 10-mile radius. Croagh Patrick, known in prehistoric times as Cruachan Aigle, is the place where, according to legend, Patrick banished the serpents from Ireland.
At the moment of the above sunset, we were looking in the direction of Slane and also Croagh Patrick, following a sacred pathway to the stars. This is breathtaking. It connects some of the most significant places associated with Ireland's national Saint, and at the same time reflects an ancient cosmology which predates Patrick by three and a half millennia. There seems no limit to what the ancients were capable of. We are amazed.