The actual history of St. Patrick is unclear. He was probably born in Britain to Roman Christian parents and, as a teenager, kidnapped by Irish raiders and sold as a slave in Ireland. Six years later he escaped and returned to Britain, where he took holy orders. He later returned to Ireland as a missionary. He was informally declared a saint shortly after his death, and by the eighth century he was widely accepted as the patron saint of Ireland.

• Catholic Encyclopedia entry on St. Patrick.

• A brief biography of St. Patrick.

Many legends have gathered around St. Patrick. It is commonly believed that he banished snakes from Ireland, even though most authorities claim that the island never had any states. He is said to have fasted for 40 days at the top of a mountain in County Mayo, which had been a site for pagan pilgrimages. He claimed the mountain for Christianity, threw a silver bell, and banished the snakes. Croagh Patrick is a popular destination for Christian pilgrims today.

Legend also says that Patrick used the shamrock to teach the Irish people about the Trinity, using it as a visual aid to explain the idea of three in one. Certainly the shamrock has been a popular symbol of Ireland for centuries. Originally the phrase "wearing of the green" meant wearing a shamrock in one's lapel. This may be how the color green became associated with St. Patrick, since in the early centuries his color was blue.

Another legend says that when St. Patrick was baptizing King Angus, he pierced the king's foot with his crozier. The crozier found at Clonmacnois and now at the Museum of Ireland in Dublin is sometimes called St. Patrick's.

• About Croagh Patrick.

• St. Patrick's crozier.

• Places in Ireland associated with St. Patrick legend.

St. Patrick's feast day is March 17, and it is commonly believed to be the day he died. It is a holy day in the Catholic Church, and a day of obligation for Catholics in Ireland.

It is also the national holiday of Ireland and a bank holiday in Northern Ireland. St. Patrick's Day is widely celebrated across the world, but the celebrations are especially large in Canada, Great Britain, Australia, New Zealand, and the United States, where there are substantial Irish populations.

The first parade held to celebrate St. Patrick's Day in the United States took place in 1761, in Boston. The first parade recorded in New York City was in 1762, when Irish soldiers paraded through the streets playing their music. They were part of the English military in the city. New York City has the largest St. Patrick's Day parade in the U.S. today; it usually has about 150,000 participants and draws a crowd of about two million people. Many other cities also have large parades and others celebrations. Chicago sometimes dyes its river green for the occasion.

• List of parades and celebrations world-wide.

• List of Irish pubs around the world.

On St. Patrick's Day, everybody wears green, because for a little while, everybody is Irish. People eat traditional Irish foods and, perhaps more important, drink Irish beer and whisky. Irish music and dancing is also enjoyed.