Similarly to Tara, the Hill of Slane`s mythology predates the arrival of St. Patrick.
According to the Dinshenchas the burial mound atop the hill is the resting place of one of Ireland`s earliest kings; Sláine. He was the leader of the Gálioin, a division of the Fir Bolg.
St. Patrick himself almost followed in the exact footsteps of the Milesians when he brought Christianity to Ireland. He arrived in Ireland a year before this journey and settled in Co. Down with his followers. In the year 433 Patrick set sail from Down on a journey that would change Ireland forever. He landed at Inbher Colpa, just as Amergin had done more than a thousand years earlier, and sailed up the Boyne. Patrick chose the Hill of Slane to announce his arrival in the Boyne Valley and Ireland. As the druids prepared to celebrate the Feast of Tara, St. Patrick celebrating Easter lit the Paschal Fire in direct defiance of the pagan ritual. The fire was observed from the Hill of Tara and the druids told King Laoghaire that unless it was extinguished that same night, it would never be put out. The King was outraged, but every time he and his druids challenged St. Patrick with their magic they were defeated. Eventually, and reluctantly, the King and his followers converted to Christianity. St. Erc, who was the only person to pay due homage to St. Patrick during the stand-off, founded a monastery on the Hill of Slane.
Patrick had established a stronghold for Christianity in Ireland that remains today and he did it by taking a journey through the Boyne Valley.