For Italian-Americans, the Feast of the Seven Fishes—a nostalgia-fueled, hours-long dinner consisting of at least seven different types of seafood—is the defining Christmas Eve tradition. Firmly rooted in Italy’s Roman Catholic background, the Festa dei Sette Pesci is a delectable blend of the sacred and secular, the old world and the new.

1. It is not a Roman Catholic feast day.

The Feast of the Seven Fishes may go hand-in-hand with Roman Catholicism, but it’s not a religious “feast day.” There is no such thing as the “Feast of the Seven Fishes” in the Roman Catholic calendar. (In fact, in Roman Catholicism, a feast day has nothing to do with gorging yourself and everything to do with reflecting on and celebrating an important aspect of the faith, often the life of a saint.) The tradition’s name merely takes after the lay definition of feast: that is, there’s a lot of food on the table!

2. Traditionally, December 24 was a day to avoid food.

In the Catholic liturgical calendar, there are special days of abstinence (where followers are advised to avoid meat) and days of fasting (where followers are advised to reduce their food intake, usually to just one meal a day). Before reforms were made in the 1960s, December 24—what Roman Catholics call The Vigil of the Nativity of the Lord—was a day to fast and abstain, with worshippers generally allowed to break the fast in the evening. The Feast of the Seven Fishes, then, seems like an obvious solution to the circumstances: You have a big, hungry Catholic-Italian family that hasn’t touched food all day. None of them are allowed to eat meat. What else is there to do but prepare a giant evening meal of pasta and seafood?

3. The tradition began in Southern Italy, but not the name.

While the tradition of enjoying a large meatless Christmas Eve meal was (and remains) common across Italy—as well as many other Roman Catholic-dominated countries—the origins of the Feast of the Seven Fishes has its roots in southern Italy. The area, which is surrounded by bountiful coastline, has been known for its seafood for generations. It's also historically poorer than the rest of Italy, with locals preferring fish because of its relative affordability.

4. The Unification of Italy ultimately helped bring the feast to America.

In 1861, the regions of the Italian peninsula joined to form a single nation. The states of the south (what had formerly been the Kingdom of the Two Sicilies) would suffer for it. The new government began allocating most of its resources to nurturing the north, causing poverty and organized crime in the south—which were already problems—to worsen. The situation plunged southern Italy into such poverty that approximately 4 million people from the region moved to America between 1880 and 1924. It’s no surprise that those immigrants took their tradition of big, fishy Christmas Eve dinners with them, making it a popular Italian-American celebration today.

5. In Italy, they would have simply called the feast La Vigilia.

Those immigrants, however, probably didn’t call it the “Feast of the Seven Fishes.” More likely, they called it some variant of La Cena della vigilia, Il Cenone, La vigilia di Natale, or simply La Vigilia. The current name of the feast—and the practice of making exactly seven types of fish—comes from the new world. “Not many people observe these numbers in Italy,” cookbook author Amy Riolo told American Food Roots. “It’s much more popular in [America]. Americans love themes.”

"As an Italian, I must admit I hadn’t heard about [the Feast of Seven Fishes] … and most of my Italian friends haven’t either," Katia Amore wrote in Italy Magazine.

6. It’s unclear what the “seven fishes” signify.

Nobody knows where the “seven fishes” moniker came from. Many insist it’s a religious symbol. The number seven, after all, appears hundreds of times in the Bible and is significant in the Roman Catholic Church: It may represent the seven sacraments. Or the seven virtues. Or perhaps it commemorates the day Christians believe God rested. Others say the number is just a good marketing tool used by restaurants. (Indeed, the earliest newspaper article we found containing the phrase “Feast of the Seven Fishes” is a 1983 advertisement for a restaurant in Philadelphia.)

7. The variety is mouthwatering.

“Talk with 10 Italian-Americans about the special feast, and you could come up with 10 dinner menus, plus a varying selection of fish,” Gerald Etter wrote for The Philadelphia Inquirer. And that’s the beauty of the feast: There are no hard and fast rules. Some people include as many as 12 or 13 dishes, including mussels in spaghetti, fried calamari, anchovies, sardines, whiting with lemon, scungilli, lobster fra diavolo, capellini with tuna sauce, branzino, sole, and shrimp scampi. Many insist on eel. (“You can’t have Christmas Eve without eel,” John Tenaglia tells the Inquirer.) Another almost universal recommendation is baccalà—dried, salted cod. But the most important ingredient, of course, is friends and family.