St. Patrick's Day is celebrated annually on March 17th, which is the anniversary of St. Patrick's death in the 5th century. According to legend, St. Patrick used the Irish shamrock's 3 leaves to explain the Holy Trinity as he spread Christianity to Ireland. The Irish have been celebrating St. Patrick's Day since the 9th or 10th century, but it was here in the US where the first St. Patrick's Day parade was first held. On March 17, 1762, Irish soldiers serving in the British military marched thro...