The person who was to become St. Patrick, the patron saint of Ireland, was born in Wales about AD 385. His given name was Maewyn.
When he was 16, he was sold into slavery to Ireland where he was a shepherd for 6 years. While in captivity he studied and turned to religion. He escaped slavery and later returned to Ireland as a missionary, determined to convert Ireland to Christianity. He used the shamrock to explain the Holy Trinity.
Patrick was quite successful at winning converts. And this fact upset the Celtic Druids. Patrick was arrested several times, but escaped each time. He traveled throughout Ireland, establishing monasteries across the country. He also set up schools and churches which would aid him in his conversion of the Irish country to Christianity.
His mission in Ireland lasted for thirty years. After that time, Patrick retired to County Down. He died on March 17 in AD 461. That day has been commemorated as St. Patrick's Day ever since.
Much Irish folklore surrounds St. Patrick's Day. Not much of it is actually substantiated. Some of this lore includes the belief that Patrick raised people from the dead. He also is said to have given a sermon from a hilltop that drove all the snakes from Ireland. Though originally a Catholic holy day, St. Patrick's Day has evolved into more of a secular holiday.
One traditional symbol of the day is the shamrock. And this stems from a more bona fide Irish tale that tells how Patrick used the three-leafed shamrock to explain the Trinity. He used it in his sermons to represent how the Father, the Son, and the Holy Spirit could all exist as separate elements of the same entity. His followers adopted the custom of wearing a shamrock on his feast day.
The holiday, March 17th, is marked by parades in cities across the United States. The largest of these, held since 1762, is in New York City, and draws more than one million spectators each year. In Ireland, it is a religious holiday similar to Christmas and Easter.