They called it the “neon sleepover.” The Route 91 Harvest Festival — three days of country music on a 15-acre lot, beneath the skyline of Las Vegas.

You could bring your kid, but no teddy bears or fireworks.

You could drink, dance and sleep in an RV park for $45 a night. Or if you preferred more expensive accommodations, maybe the towering Mandalay Bay hotel next door.

Luke Bryan once called Route 91 an “adult playground,” Rolling Stone wrote. And the lineup for its fourth year was “stellar.”

Eric Church would headline on the first night — black leather, loud guitars and big drums.

Then, on Saturday, Sam Hunt, before a sold-out crowd of tens of thousands.

And then the third night, which in many ways has not yet ended.

Friday

A couple got engaged to the lyrics of High Valley’s “Make You Mine” in the late afternoon, while electric fans blew mists of water into the crowd beneath the fierce Nevada sun.

By nightfall, revelers covered the field in front of the main stage, a shimmering mass of people under spotlights.

“One for the books,” Brothers Osborne wrote on Twitter.

When Church took the stage for the main act, a skull flashed on the drum beside him.

Saturday

“We can’t believe we get to do it all over again,” trumpeted the festival’s official Twitter account as the crowd returned for the second-day lineup. Passes had long ago sold out, but one fan got in courtesy of a golden can of Budweiser:

“Never know what surprises await.”

Brett Young played that day. And Lauren Aliana. And Bobby Jones and the Raging Idiots.

As Hunt prepared to take the main stage, the crowd pressed up against the fences and the hotels behind them shone like gems in the night.

Sunday

On the final day, a man with a gun waited and watched from one of those hotels, the Mandalay.

A police SWAT team would rush his room on the 32nd floor, but only after he’d unleashed a stream of constant, rapid gunfire in what may be the worst shooting in modern U.S. history.

His bullets injured hundreds and killed at least 50. The suspect was found dead, police said.

But before that horror came music.

The penultimate act, Jake Owen, had brought his crew and manager, a friend celebrating her 50th birthday.

The singer later reflected on NBC’s “Today” show about how much he took for granted.

“We live this life of not being scared,” he said. “Which I think is great.”

He went through his set, and then walked onto the stage with a couple of friends to watch Jason Aldean perform the final set on the festival’s final night.

“Is that gunfire?” he remembered thinking, and then being sure it was.

Shot after shot, faster and faster, for he was sure was 10 straight minutes.

“You could hear it ringing off the tops of the stage,” Owen said.

Aldean was barely five measures into “When She Says Baby” when shots began ringing out from above.

The gunfire continued, steady against the beat of the song, as Aldean crooned:

“It’s tough just gettin’ up/

“Throwin’ on these boots and makin’ that climb/

Some days I’d rather be a no-show . . .”

Then, the band abruptly stopped playing.

Aldean was seen in social-media videos sprinting off the stage.

And Owen and the other stars, and all the thousands of spectators at the fourth annual Route 91 Harvest Festival, were fleeing and screaming and falling and dying.

The night would go on, but the music was done.