St. Patrick first came to Ireland as a slave and became a devout Christian during his captivity.

St. Patrick’s Day is best known for parades, beer, and turning rivers green, but the holiday has a long history that’s more somber than its current incarnation.
Saint Patrick
St. Patrick was born around 387 C.E. in Scotland, and turned to God once he was kidnapped by slave traders and brought to Ireland to be a shepherd.
“The love of God and his fear grew in me more and more, as did the faith, and my soul was rosed, so that, in a single day, I have said as many as a hundred prayers and in the night, nearly the same,” he wrote, according to Catholic Online. “I prayed in the woods and on the mountain, even before dawn. I felt no hurt from the snow or ice or rain.”
He joined the priesthood after his escape at the age of twenty, and eventually became a bishop. Patrick was tasked with the mission of bringing Christianity to Ireland, where he was enormously successful in converting much of the mainly Druid and pagan population.

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St Patrick’s stone on the Hill of Tara.

History
St. Patrick’s Day originated as a Roman Catholic holiday recognizing St. Patrick, and was brought to America by Irish immigrants as a way of affirming their identity. It’s since been adopted by Americans of all backgrounds.
Traditions
Some Catholics celebrate St. Patrick’s feast day by going to mass, while other observers of the holiday wear orange and green and eat cabbage and corned beef. St. Patrick’s Day parades are commonly held in many cities.

Youngsters hold flags as they watch Irish pipers move up Fifth Avenue in the annual St. Patrick’s Day parade in New York, March 17, 1949.

Symbols
The shamrock is associated with St. Patrick, as he reportedly used the three-leafed plant as a way of explaining the Trinity — Father, Son, and Holy Spirit.