An NFL stadium converted into the biggest natatorium the world has ever seen.

A quadrennial swim meet that, in no small part thanks to the star power of Ledecky and a handful of teammates, has grown so large as to require an NFL stadium to contain it.

And Ledecky’s own transformation, over the course of 12 memorable years on these stages, from teenage sensation to legendary icon.

On the opening night of the nine-day trials, where Team USA will pick the squad that will head to Paris next month for the Summer Games, she powered through the eight lengths of the 400 free in 3 minutes 58.35 seconds, winning by nearly four seconds and clinching a spot on her fourth Olympic team. Paige Madden (4:02.08) was the runner-up and earned the second berth in Paris.

It was a night for the women’s side of Team USA to reassert its international prowess, with Gretchen Walsh making the night’s biggest statement. In a semifinal of the 100-meter butterfly, Walsh went out fast and came back fast, shattering the world record — set eight years ago by Sweden’s Sarah Sjostrom — with a time of 55.18 seconds, a swim accompanied by a roaring crescendo not unlike the sound of a crowd during a 99-yard touchdown run. Sjostrom’s time in 2016 was 55.48.

Walsh, a 21-year-old Nashville native and University of Virginia star, was a bundle of emotions afterward, holding back her tears with one hand over her face and waving to the crowd with the other.

“I didn’t think I was going to [set the record] today,” Walsh said. “… And now here I am, the world record holder. It’s, like, actually insane. I think I was the most shocked of anyone I know.”

In the only other final Saturday night, the men’s 400 free, local favorite Aaron Shackell won in 3:45.46 to become a first-time Olympian; Kieran Smith, Ledecky’s teammate at Gator Swim Club in Gainesville, Fla., was second in 3:45.76. After climbing out of the pool, Shackell spiked his swim cap and goggles and let loose a scream.

Though record-keeping is suspect at best, USA Swimming believes Saturday night’s attendance of 20,689 set a record for a swim meet, topping the peak of roughly 16,000 who turned out for the 2016 Rio de Janeiro Olympics. Part of the motivation for supersizing the trials — moving it from a basketball arena in Omaha, where it resided from 2008 to 2021, to the home of the NFL’s Indianapolis Colts — was to shatter that record. Consider it shattered.

It was a spectacle worth soaking in, even for elite athletes whose game faces typically don’t permit such reflection. As Ledecky emerged from the tunnel onto the pool deck for the 400 free final — to a deafening chorus of pounding music, throaty cheers and adolescent squeals — she made a point to look around the stadium, delighting in an atmosphere unlike any she had experienced in her long career.

“It’s incredible. I think tonight blew it out of the water,” Ledecky said of the atmosphere in the stadium. “It’s the kind of energy I’d never felt in a major meet. I was kind of blown away walking out there and seeing all those fans.”

Half a lifetime ago, on June 26, 2012, in Omaha, Ledecky dived into the pool at an Olympic trials for the first time, also for the preliminary heats of the 400 free. At 15, she was the youngest swimmer in her heat by nearly a year and a half. The heat sheets, meet program and television broadcast back then listed her first name as “Kathleen.” Those trials, like the ones in 2016 and 2021, took place in a converted basketball arena with a capacity of around 13,000.

Ledecky, at the time a rising sophomore at Stone Ridge School in Bethesda, fell short of earning an Olympic berth in the 400 but five days later won the 800 free to punch her ticket to the 2012 London Games. There, as the youngest swimmer in the final by some four years, she stunned the sport by winning the gold medal, the start of one of the most storied Olympic careers of this generation.

Ledecky’s longevity, coupled with her sustained excellence, has her on the verge of all sorts of history this summer. Two more gold medals in Paris, for example, would vault her past fellow American Jenny Thompson for the most in Olympic history by a female swimmer.

The 400 free is Ledecky’s third-best event, behind the 1,500 and 800, and she is no longer considered the best in the world at that distance, an honor that goes to defending Olympic champion and world record holder Ariarne Titmus. But on American soil, Ledecky’s dominance in the 400 is unquestioned.

She has now gone under four minutes in the 400 free 30 times in her career. Every other American female swimmer in history, combined, has done so zero times.

With the U.S. trials among the latest on the worldwide calendar, the Americans competing here have the benefit — or perhaps the added pressure — of seeing what times their international rivals posted in their own trials.

In the case of Ledecky, by the time she dived off the blocks for Saturday’s 400 free, she already knew Canada’s Summer McIntosh had swum a 3:59.06 and Australia’s Titmus had turned in a scorching 3:55.44, the second fastest of all time, at their national trials.

“I keep track of everything going on around the world,” Ledecky said. “I know what everyone’s going, and I’m excited to race everyone.”

Ledecky, McIntosh and Titmus have held the 400 free world record within the past 25 months, with Titmus taking it from Ledecky, McIntosh taking it from Titmus and Titmus taking it back with a 3:55.38 last summer at the world championships in Fukuoka, Japan. In that race, Ledecky (3:58.73) finished a distant second, while McIntosh (3:59.94) faded to fourth. The head-to-head-to-head rematch in Paris this summer is already taking on race-of-the-century-type hype.

Although Titmus appears to have put some distance between herself and her rivals, count Ledecky out at your own risk. In 2016, at the pinnacle of her powers — the summer of her five-gold-medal, two-world-record performance in Rio — she swam a 3:58.98 in the 400 free at trials. A month later in Brazil, she went 2½ seconds faster, earning the gold medal and the world record.

Comparing the 2016 trials to the 2024 edition, she is faster this time. She thinks she still has another monster 400 free left in her. She has about six weeks left, before the Paris Games arrive, to summon it.