On Saturday, millions of people around the world will celebrate Saint Patrick's Day, which honors Patron Saint(a main religious figure)of Ireland. Communities across the United States will host parades , parties, and other festivities to mark the occasion. 

This year, cities like Boston, New York, and Chicago have organized big events celebrating Saint Patrick's Day. In New York City, hundreds of thousands of people will gather to watch the Saint Patrick's Day parade-the nation's largest. It is one of the most watched parades in the world. Last year, almost 2 million watched it , more than 150,000 took part in it and they filled the streets. The parade, first held in 1776, is also one of the oldest. 

Chicago also throws a big celebration. Every year, the Chicago River, which crosses the city, shines green as event organizers pour about 40 pounds of fluorescence, a powerful dye , into the water. 

Boston keeps its parade rolling for three hours or more. It is the nation's second-largest parade. The city will also show respect to one of its most famous former residents, President John F. Kennedy, by opening the exhibit "A Journey Home:John F. Kennedy and Ireland", at his official library. 

Patron Saint lived in Britain in the early fifth century, when it was still part of the Roman Empire. He was caught and sold into slavery in Ireland when he was only 16. He finally escaped slavery and turned to a life of religious devotion. He trained to become a minister and set out to spread Christianity throughout Ireland. After 30 years as a religious leader, Patrick died on March 17, 1461. Saint Patrick's Day is always celebrated on March 17. In Ireland, it is an official holiday.
When was the first one  held there?
The parade, first held in 1776, is also one of the oldest. 