St. Patrick’s Day—just another excuse for decent folk to get shitfaced and deface the world with obscene amounts of green. But that saint part isn’t in the title for show: Saint Patrick was a real dude who roamed around Ireland in the 5th century spreading Christianity to the pagan Druids. So how did a chaste saint influence a now not-so-chaste day of celebration? Join me for a little historical adventure.

Saint Patrick was like most saints: pious and devout. Born Maewyn Succat in Roman Britain, he was captured by Irish bandits at the age of 16, and sold to a druid in Ireland. For the next six years, he lived as a slave before a mysterious voice told him to escape. It said, “Very soon you will return to your native country. Look, your ship is ready.” Patrick diligently followed this voice, walking a measly 200 miles across the Irish countryside to catch a (pirate) ship back to Britain.

He then headed over to France for formal priesthood training and eventually left as a bishop, with instructions from the Pope to return to Ireland and convert the Irish peoples to Christianity. He spent the rest of his life wandering Ireland, converting everyone he could, and while it’s not clear what year he died—460 or 493 A.D.—historians all agree on the day he died… March 17th.

Fun Fact: He was also the first person ever to publicly condemn slavery.

How did we get from saintly Patrick to intoxicated Shamrock Day?

It wasn’t until 1000 years after his death that Luke Wadding (just some scholar) would champion the church to put an official feast day on the liturgical calendar. Even then, March 17th continued to be a minor holiday in Ireland until the 1970s.

Blame America for really revving up the green themed party (some even argue that St. Patrick’s Day was actually invented by Irish-Americans). Back when there were only 13 colonies, the first St. Patrick’s Day parade was held in New York City as a nod to Irish soldiers serving in the English military and, by 1848, it had grown to be the largest parade in the world. In America, St. Patty’s Day started and continues to be not just about the religious aspect of Saint Patrick, but a celebration of Irish heritage. How does this translate into green beer, green rivers and this?  Your guess is as good as mine.

Ireland has since come around, making it a public holiday (1903), making a law that forced bars and pubs to close for the day (1905), repealing said law (1970s), and finally creating their own St. Patrick’s Day Festival (1996) that sprawls for five days.

But why all the green?

The symbolism of the green comes from an anecdote about good ol’ Saint Pat. It is said that he taught the concept of the holy Trinity with a three leafed shamrock. The green of the shamrock then became associated with Irish Catholics. Since Ireland’s population is predominantly Catholic, this spread throughout the world, inexorably linking Ireland with green. It also helps that Ireland is literally green themed (cough: rich green landscape), hence its nickname the “Emerald Isle.”

Fun Fact: St. Patrick’s Day was originally associated with the color blue (St. Patrick’s blue), the connection being Ireland’s coat of arms which are blue and gold.

Extra Credit: The green in Ireland’s flag symbolizes Catholics while the orange is associated with Protestants (William the Orange), and so when the flag was adopted in 1919 it was meant as a sign of peace between the two factions.

Wait, St. Patrick’s Day is not always on March 17th?

Mostly, but no. When St. Patrick’s Day falls during Holy Week (the final week of Lent) it gets booted to a later date because solemnities are more important than feasts. Most recently it was moved in both 1940 and 2008 for this reason, but don’t worry: it’ll stay on the 17th for another 150 years (until 2160). And this only really counts if you’re celebrating the religious aspect of the holiday rather than the cultural one.