St. Patrick's Day.

This tradition is celebrated on March 17 in the republic of Ireland, Nothern Ireland, Newfoundlandand, Labrador and Montserrat, and is also celebrate in some countries of America (Canada, the United States, Argentina etc). Is the anniversary of the saint’s dead, in this day commemorates St Patrick and de arrival of Christianity in Ireland, also is celebrated the heritage and culture of ireland in general. Irish people have this day as a religious holyday for over 1000 years. The prohibitions are: the consumption of meat, dance, drink and feast.

Is celebrated with parades and public festivals, “ceilithe” and most traditional is to use green clothes or spades.

The legend say that St Patrick used the three-leaved shamrock to explain the holy trinity to Irish pagans, one of his methods of teaching was the use of the shamrock to explain the Christian doctrine of the trinity to Irish people, and after nearly thirty years of evangelism, he died on 17 March 432, accorded to the legend he was buried at Downpatrick.

http://news.nationalgeographic.com/news/2012/03/120316-saint-patricks-day-2012-march-17-facts-ireland-irish-nation/