Wells Fargo historian Heidi Berg, foreground, reads Saturday to a group of children at The Library of Congress National Book Festival, held at the Walter E. Washington Convention Center in Washington, D.C. (Nikki Kahn/The Washington Post)

For the die-hard book lovers of Washington, the Mall was the perfect place for the celebrated National Book Festival, the largest festival of its kind in the country. There was a certain magic, festivalgoers said, as people wandered by and became entranced by one author or another and decided to stay. There were times that agitated protesters nearby fell under the spell of a good story and put down their signs to listen.

When the National Park Service decided to put a premium on preserving the grass on the nation’s front lawn, organizers of the festival, run by the Library of Congress, decided to move indoors. And they held their breath that the magic would not be lost.

The question on everyone’s mind was: Would it work?

On Saturday, the festival had several strikes against it going in: A long holiday weekend when many people were out of town. One long 12-hour day instead of a two-day festival. Metro track work. And nostalgia for the raucous, picnic-like atmosphere on the Mall. Then as thousands upon thousands of readers of all ages filled the cavernous conference halls at the Walter E. Washington Convention Center — and lined up to buy books signed by their favorite authors — organizers let out a collective sigh.

It worked.

Braelyn Bryant, 5, pays rapt attention to a book reading at the Wells Fargo Stagecoach during the The Library of Congress National Book Festival on Saturday. (Nikki Kahn/The Washington Post)

“The crowds are huge. I mean, they’re huge. And we’re very gratified by that,” said Jennifer Gavin, one of the festival organizers. “The author pavilions are almost full. We have 900 seats in fiction and mystery. Full. History and biography, 1,000 seats. Nearly full. The children’s activities are mobbed.”

A standing-room-only crowd watched former Supreme Court justice Sandra Day O’Connor interview her brother H. Alan Day and his co-author on their book about wild horses. A capacity crowd strained to hear Georgia Democratic Rep. John Lewis recount life during the civil rights protests and the comic book he wrote about it, “March.” Kids flocked to hear David Pilkey, author of the Captain Underpants series, and laughed uproariously at teen author Kate DiCamillo.

And even Eric Cline, a professor of classics and anthropology at George Washington University, drew a full house to hear his talk about the collapse of civilization in 1177 BC.

“We were all worried about the change of venue, worried that we’d lose that magical element of serendipity from being on the Mall,” said Marie Arana, who sits on the festival board of directors and is a former book editor at The Washington Post. (The Post is one of the festival’s sponsors.) “But it feels every bit as large, with the exception that we don’t have people standing in the rain.”

Last year, more than 200,000 book lovers flocked to the festival, a testament to Washington’s stature as the largest market for hardcover books in the country. Organizers will be tallying numbers over the coming days.

Perhaps children wouldn’t be rolling around outside in the grass and the indoor convention center felt more like a subdued conference. But Arana said she hoped festivalgoers would still be drawn by the magic — the power of sharing diverse stories that help us understand what it is to be human and speak to our souls.

Bob and Susanne Morris weren’t sure at first. The retired D.C. couple are die-hard festivalgoers, braving heat, humidity, rain and bigger crowds every year since its founding in 2001.

“We immediately decided it’s so much better,” said Bob Morris, 77, a retired communications management trainer. “We’re able to attend so many more events. In previous years, you couldn’t hear very well, or there were just too many people in a tent.”

Susanne Morris, 76, who worked as a trainer as well, agreed. The diminutive Morris said she often had trouble seeing in the crowded tents on the Mall, and, if she didn’t get to a session early to get a seat, she spent most of her time standing, craning her head to get a glimpse of the action.

And rather than rows of portable toilets, and the whims of weather, there are now plenty of indoor bathrooms and air conditioning.

Becky and Megan Rast were just leaving the talk by author E.L. Doctorow, who explained that writers need to break the rules and, as poet Ezra Pound said, “make it new.”

This is the first National Book Festival for Megan, who moved to the D.C. area two years ago and works for an international nonprofit, and her mother, Becky, a retired high school teacher who was visiting from Atlanta. The fact that it was indoors made no difference to them.

“We’ve been to lots of book festivals in other places, and they’re all indoors, so this is nothing new,” Becky Rast said. “To me, it’s hard to have a bad book festival.”

Longtime festivalgoer Iris Hernandez, 44, a pediatrician and mother of Damian, 7, said she was initially disappointed by the move indoors but never considered not coming.

Hernandez sat on a blue carpet in the kids’ section as Damian, in a small red beanbag chair was absorbed in his book, “Star Wars: Jedi Academy, Return of the Padawan.”

“Honestly, it was nice to be outside, but we’ve adapted,” she said. “I’m more disappointed that it’s only a day.”

But on the plus side, she said, patting the carpet, “No grass stains.”