St Patrick´s day is celebrated each year on March 17th, in honour of St Patrick, the patron Saint of Ireland.He brought Christianity to the Irish. According to legend, Saint Patrick used a shamrock to explain about God. The shamrock has three leaves on each stem. It simbolizes the idea of trinity. People usually wear something green. Watch this ppt on slideshare to know more about the legend and history of this saint. You can also watch a video from you tube I published in my blog for the 1st cycle. Click here.