Sunday marks Cinco de Mayo 2019. This year, you can mark the occasion locally at a taco-fest in Providence, a Boston Harbor Cruise, or a pub crawl in Faneuil Hall — to name just a few options. Over the years, Americans have embraced this Mexican holiday — margaritas in hand — and devised an array of ways to celebrate it.

But when it comes to what it is we’re actually celebrating, we’re a little less clear.

I recently asked a range of people, from friends to colleagues to passersby, if they know what Cinco de Mayo celebrates. By far the most common guess is Mexican Independence Day.

That guess is incorrect. Mexican Independence Day falls on Sept. 16.

Cinco de Mayo celebrates Mexican troops' victory over the French in an 1862 battle.

At the time, Mexico was emerging from an expensive civil war that left them in debt to European powers of the day, including France. France sent troops to Mexico to get its money, and then decided it would try to take the whole country. On May 5, 1862, advancing French troops were met by an ad hoc Mexican force in the state of Puebla — a classic David vs. Goliath scenario.

"This ragtag army of mostly indigenous peoples and ordinary citizens were able to defeat the French troops, which were considered at the time the ultimate fighting power in the world," said Andres Resendez, professor of history at the University of California, Davis.

Even though France did eventually occupy the country and briefly ruled Mexico, the Mexican victory in the Battle of Puebla became a symbol of resistance and a source of regional pride.

"It is, however, not a national holiday or anything like that," said Resendez. "It's a historic milestone. It is remembered in Mexico, especially in Puebla."

Puebla is where East Boston's Louis Garcia — who owns and operates Angela’s Café with his brother and mother — was born and raised.

"What makes me ... proud is that people are celebrating a Mexican holiday in the United States," he said. "They're getting to know Mexico more."

Garcia said he has fond childhood memories of Cinco de Mayo in Puebla, as a day-long party and a day off from school.

"It’s basically a huge holiday in Puebla," he said. "It’s like a huge parade. It lasts probably like five hours."

While Cinco de Mayo celebrations in parts of the U.S. — including in Southern California and Texas — stretch all the way back to the years just following the Battle of Puebla, the real explosion in its popularity here has come in recent decades, with a hefty assist from brands like Jose Cuervo and Corona. Today, Cinco de Mayo is celebrated more widely in the U.S. than it is in Mexico. And, like St. Patrick’s Day was for the Irish, Cinco de Mayo been reinvented here as a kind of generalized celebration of Mexican culture.

"It feels a little random," said Boston resident Edgard Hernandez Reyna, who was born and raised just east of Puebla, in Veracruz. "Out of all the dates, why choose this one?"

Hernandez Reyna said when he first came to Boston in 2014, he found the Cinco de Mayo celebration here in the U.S. a bit mystifying, like if Mexicans were to decide to celebrate "America Day" on the anniversary of the Battle of Bunker Hill. Still, he said he's embraced it, and hopes Americans will continue to as well.

"Take it as a day to learn something new," he said. "And party, yes. Go for it. Because Mexicans do party. You guys could learn a thing or two from our way of partying. And during the party go meet someone from Mexico and talk to them. See how their life and your life are similar or different."

And if you do find yourself at a rip roaring party this Cinco de Mayo, do try and exercise some discretion. As sure as spring follows winter and the dawn follows the dark, six follows five. And this year, May 6 falls on a Monday.