Everyone knows on St. Patrick’s Day we wear green, decorate with shamrocks and eat corned beef and cabbage. But how much do you know about the origins of the holiday? Here are five things to know about how St. Patrick’s Day became the holiday we know today.

St. Patrick’s Day is the official feast day for the patron saint of Ireland in the Catholic church.

St. Patrick died on March 17, 461. He’s the patron saint of Ireland, but he isn’t even technically Irish. At the age of 16, he was kidnapped into slavery from his home in Britain and brought to Ireland. He escaped and fled to a French monastery, where he converted to Christianity and decided to return to Ireland as a missionary. The church established the saint’s feast day in 1631.

Shamrocks represent the Holy Trinity: God, Jesus and the Holy Spirit.

Legend has it St. Patrick used a shamrock to explain the Holy Trinity while doing missionary work, since a shamrock has three leaves. However, the origin of the legend is widely disputed.

St. Patrick’s Day became a larger secular celebration when Irish immigrants came to the United States.

The Christian feast day morphed into a secular holiday when U.S. cities with large amounts of Irish immigrants began throwing parades and other celebrates.

Boston held the first St. Patrick’s Day parade in 1737.

Boston, which was home to many Irish immigrants, was the first American city to celebrate the holiday with a parade. New York City held its first parade in 1762.

Today, more than 100 St. Patrick's Day parades are held across the U.S., but Boston and New York City have the biggest celebrations.

Blue was originally the color associated with St. Patrick.

Blue was featured in Irish flags as well as the royal court, but green became associated with the holiday during the Irish Rebellion in 1798. The British wore red and the Irish wore green, and green became the color associated with Ireland and st. Patrick’s Day ever since.

In modern St. Patrick’s Day celebrations, revelers color beer green and wear the green, and Chicago has even colored its river green to mark the holiday since 1962.

Read more: Why do people wear green on St. Patrick's Day?