Saint Patrick's Day is celebrated on March 17th to honor Saint Patrick, the patron saint of Ireland. Saint Patrick used the three-leaved shamrock to explain the Holy Trinity to Irish pagans when he introduced Christianity in the 4th century. Symbols of Saint Patrick's Day include shamrocks, leprechauns, and the Blarney Stone. The holiday is celebrated worldwide with parades, wearing green, drinking green beer, and eating traditional Irish foods like beef and cabbage.