The Hill of Slane
It had long been known as sacred ground when St. Patrick visited the hill on the eve of Easter in 433 A.D. He lit a Paschal or Easter fire which could be seen from the nearby hill of Tara, the royal seat of power. There, a fire also burned to clebrate the pagan feast of Beltane. Since it was against the law to light any fire in the area while this was taking place, Laoghaire, the king at that time, was furious and rode off with his retinue to arrest the mystery rebel. Miraculously – some say through an earthquake, others by holding up a shamrock- St. Patrick convinced the king of his belief in Christianity and the power of the Holy Trinity. It was a power that St. Patrick thought would be useful to the king who only wished that his soldiers could be as brave as St. Patrick and his followers. He took the group prisoner and marched them back to the Hill of Tara. The next day, they were spared and were allowed to preach Christianity to the pagan army. Today, at the top of the hill are the ruins of a Franciscan Monastery built in 1512.
Situated in the Braid Valley near Ballymena,Co. Antrim, Slemish Mountain is approximately 1,500 ft above sea level. Ireland’s patron saint is thought to have walked these slopes for six years after being taken into slavery at the age of 16. He worked for a master named Miliucc, herding swine and sheep. And according to his writings, it was here that St Patrick turned to prayer as his only consolation. He escaped, became a priest and began his mission to convert the Irish to Christianity. Wild flowers, some rare, grow on the grassy slopes. From the top, if you look north, you will see the ruins of Skerry Church on a hilltop where Miluicc’s fort once stood. This was the ancient burying place of the O’Neill’s of Clandeboye. Slemish is still a place of pilgrimage in memory of Saint Patrick on his feast day – 17 March.
 Copied from Irish Customs and Culture: http://www.irishcultureandcustoms.com/CultureCorner/CultureCorner.html