On a frigid Saturday night in January, more than 400 people have packed the cavernous sanctuary of St. Stephen and the Incarnation Episcopal Church in Columbia Heights — but not to sit quietly and chant hymns and prayers. These folks are clapping, tapping their feet, smiling and moving briskly to the sounds of old-time music played by a five-member band. These folks are square dancing.

They’re dancing in pairs and in two-couple squares. They’re circling left. They’re circling right. They’re swinging their partners roundabout. “Bird in the Cage!” shouts the caller from the stage, and three dancers circle a fourth.

“The beauty of square dancing is someone tells you what to do,” says Gabriel Popkin, a co-founder of the DC Square Dance Collective who’s also one of tonight’s callers. “You don’t have to worry about moves because the caller calls out each figure. It’s not highly choreographed, and you don’t need to master complex steps.”

Square dancing is also multigenerational and doesn’t require fancy dress. The crowd this night includes men and women of all ages, with white hair and long tresses, clad in plaid shirts and jeans, skirts and dresses, running shoes and high heels. And anyone can ask anyone to dance. “Gender doesn’t matter,” says Lucia Schaefer, 29, an elementary school music teacher who’s also a caller.

Square dancing is an American folk dance that incorporates elements of Scottish and Irish reels, English country dances, French cotillions and quadrilles, and West African and Native American dances, says Phil Jamison, a professor of traditional music and dance at Warren Wilson College in Asheville, N.C. It’s “a way to build community. You hold hands with people you don’t know. That brings people together and creates a bond,” Jamison says. “I think that’s important today given the current social and political divide in America.” No one here would disagree.

There’s always live music at the group’s square dances. Specifically, old-time music, “old time” being the name of the musical genre associated with square dancing. On this night, Slow Down Tommy is onstage with Marty Frye on Irish flute, Anders Fahey on banjo, Jonathan Een Newton on fiddle, David McKindley-Ward on guitar and Noah Bowman on double bass. Old-time music hails from Appalachia and “is the predecessor to bluegrass,” Newton tells me.

Although he grew up in Kentucky, the 38-year-old Popkin would seem to be an unlikely candidate for founding a square-dancing tradition in the nation’s capital. A resident of Mount Rainier, Md., he’s a science and environmental writer. (His work has appeared in The Washington Post Magazine, among other outlets.)

“I had no exposure to dance growing up,” he says. “I went to a few high school dances, but it wasn’t a thing.” After graduating from Wesleyan University in Connecticut with a major in physics, he moved back to Kentucky, where a friend invited him to a contra dance, a folk dance related to square dancing that involves two facing lines of dancers. That’s when the bug bit. Soon he was square dancing whenever he could. “I liked it enough to keep doing it,” he says understatedly.

In fact, he liked it so much, he began to organize some dancing on his own. The first square dance he put together took place in the kitchen of his Louisville farmhouse. By 2008, he’d moved to the D.C. area. “I wanted to meet dancers, so I Googled people who did contra and square dancing,” he says, but he soon realized that “there wasn’t much of a scene.” So over the next two years, he organized a half-dozen or so public dances. “Most were fundraisers for some group or another,” he says, but “a few were just dances for the sake of dancing.” He also organized dances in his home.

One of his co-founders, Janine Smith, a 64-year-old cardiac nurse practitioner, gestures to the crowded floor. “This whole dance started in Gabe’s living room,” she says. “He had amazing parties with musicians and dancers. There was enough room for one square in the living room and one in the dining room.”

In October 2010, about eight people met for the first time at a restaurant in Takoma Park, Popkin recalls. “We just started calling ourselves the Collective and organized one dance at St. Stephen’s on February 26th, 2011, to see if anyone would come.” The group advertised on Facebook and via email and put up a few signs in the neighborhood.

“We booked the small backroom, but when we got there, the church staffer told us they’d mistakenly double-booked that room, so they told us to use the sanctuary,” says Smith. “We moved a few pews to make enough room to dance. And then 200 people showed up! It was divine intervention.”

Since then, the collective has been organizing square dances regularly. “But we’ve always been kind of informal. We’ve never had a board or designated roles other than treasurer,” says Popkin. The group only recently created a website.

Informal it may be, but there’s no question who’s the backbone of it all. “Gabe is passionate about dancing. He’s a quiet, unassuming, behind-the-scenes guy, but he’s the mastermind,” says Smith. “He insisted that our public dances be accessible by Metro and bike and that it be cheap.” (Admission is $5.)

Popkin shrugs modestly. “People have been dancing since there were people,” he says. “It’s the most basic thing.” And he heads off to join a square.

Audrey Hoffer is a writer in Washington.