Saint Patrick's Day is celebrated on March 17th to honor Saint Patrick, a 5th century priest born in Scotland who introduced Christianity to Ireland. According to legend, Saint Patrick used the three-leaf shamrock to explain the Holy Trinity and drove all the snakes out of Ireland. The Irish celebrate with parades, costumes, and festivities. Leprechauns are mischievous fairies from Irish folklore that possess a pot of gold. Americans also celebrate with parades, dancing, and dyeing rivers green.