Despite the popular myth, St. Patrick did not banish all the snakes from Ireland. In fact, being an island nation, there never were any snakes in Ireland at all.
But Patrick was significant in that he converted thousands of native Irish to Christianity.
He was born in 385 in Britain and was captured by the Irish when he was 16 and forced to work as a shepherd, where some say he had a vision to convert more of the Irish to Christianity. After six years in captivity, Patrick escaped. He traveled to France, where he underwent religious training at Auxerre. He was ordained as a priest in 432 and returned to Ireland.
There, Patrick tried to weave the Irish people's pagan rituals with Christianity. According to legend, Patrick set a bonfire on a hill near the town of Tara to celebrate Easter. The pagans were accustomed to using fire to honor their gods, and his action gained their respect. Patrick is also credited with adding a circle to the cross to symbolize the sun, an familiar image in Irish lore.
By the time Patrick died on March 17, 461, the majority of Irish had converted to Christianity.
For hundreds of years, Saint Patrick's Day remained a religious holiday. Surprisingly, the first St. Patrick's Day parade was held not in Ireland, but in New York City in 1762, when Irish soliders in the British army decided to honor their homeland.
When the Potato Famine hit Ireland in 1845, millions of Irish died from starvation, and millions more decided to escape the hardship and emigrate to the United States. Today, over 37 million Americans claim to be of Irish heritage, and the celebration of St. Patrick's Day has evolved into a celebration of anything Irish.
In fact, St. Patrick's Day has been so Americanized that Ireland didn't start celebrating the holiday in force until the 1990s. The Emerald Isle now has about 30 parades, as opposed to the 100 or so parades held every year in the United States.