For the better part of the past decade, Sin City’s rallying cry has been “what happens in Vegas, stays in Vegas,” but that has gone out the window — along with the notion of music as a loss leader in a town built on gambling. Since Caesars Palace launched the Colosseum in 2003 for Celine Dion’s “A New Day” residency, such stars as Britney Spears, Elton John, Rod Stewart, Mariah Carey, Jennifer Lopez, Queen, the Who and Gwen Stefani have all undertaken high-profile multi-date casino engagements in Las Vegas. Spears recently signed for a reported $500,000 per show to leave Planet Hollywood’s Zappos Theater, which is part of Caesars, for the rival Park Theater at Park MGM, which also announced Lady Gaga and Aerosmith for their own stays beginning later this year and next.

Former resident journalist Corey Levitan points to George Maloof opening the Palms Casino in 2001, followed by Caesars’ Planet Hollywood, as factors in Las Vegas flipping the script to become a hip destination.

“Millennials have no idea Vegas isn’t supposed to be cool,” says Levitan. “There’s nothing negative about it for them. Of course, they don’t gamble as much, either. The casinos have to find a way to redefine the city to capture that market. And music seems to be one way that might work.”

As longtime area concert promoter Danny Zelisko notes, new arenas including the Mandalay Bay Events Center and MGM Grand Garden Arena in the ’90s provided an alternative to the Thomas & Mack Center, with the T-Mobile Arena opening in 2016 for the NHL Golden Knights’ inaugural season, and the much-ballyhooed MSG Sphere from Jim Dolan and Irving Azoff slated for 2020.

Perhaps the city’s top residency is EDM superstar Calvin Harris at Caesars’ nightclub property Omnia, where he makes approximately $1 million a show in a reported $280 million deal. Electronic music has been attracting younger audiences to the desert since the Electric Daisy Carnival moved to Vegas permanently in 2011.

Seth Yudof is an independent concert promoter whose UD Factory books a number of shows into Las Vegas, including “I Love the ’90s,” a rotating lineup featuring Salt-N-Pepa, All 4 One, Kid N’ Play, Blackstreet and En Vogue, which plays regularly at Caesars’ 1,400-capacity Paris Hotel & Casino. He identifies some of the city’s breakout acts, including Imagine Dragons — which started out as a Strip cover band — the Killers and Panic! at the Disco, as raising Las Vegas’ profile as a music center and making it a desirable place to play.

“Las Vegas has always been the home of new and emerging artists doing new music in their prime, from Sinatra to Elvis Presley,” Yudof says. “When Louis Prima was playing free shows in the lounge at the Sahara, it was the same year he won a Grammy.”

Rob Prinz, ICM co-head of worldwide concerts, is given credit for Celine Dion’s groundbreaking residency at Caesars Palace, a concept that reversed the idea of touring. “Instead of traveling around the world putting on concerts for your fans, they come to see you,” says Caesars President of Entertainment Jason Gastwirth, who booked Spears at Planet Hollywood in 2013. “It takes a certain kind of artist, one with a wide-scale fan base, a great music catalog and who’s capable of bringing it every night. A good rule of thumb would be, they’re identifiable by one name.”

With Vegas’ booking carved out by Live Nation, AEG and Caesars Entertainment — the three largest concert promoters in the world — the landscape has become increasingly competitive, with the high-profile residencies becoming a major selling point. “They’ve proven a boon to both artists and fans,” Gastwirth says. “We’ve formed a great partnership which has enabled them to move beyond the traditional touring model.”

“What the residencies do is market your brand throughout the year, even if you’re only performing a limited number of dates,” notes UD Factory’s Yudof. “Your presence in this city is greater than any other place you could go to.”

From Wayne Newton and Engelbert Humperdinck to Elton John and John Fogerty, Las Vegas has always been a town of multi-date engagements.

“They didn’t call them residencies back then,” Zelisko says. “The genres of music have evolved over the years, and so have the audiences. Vegas used to be typecast as a place for old acts. But that’s not the case anymore. ”

Casino entertainment is no longer an afterthought, either. According to the Las Vegas Convention and Visitors Authority, it’s entertainment — not gambling — that’s the No. 1 reason people come to the city. And a new football team is on the way so the crowds are bound to grow.

“Every department and every aspect of the casino has a bottom line,” says Yodof. “Back in the mob-run days, the concern was just making money overall, which is where you got the free music and cheap food. They just wanted warm bodies in the casinos. These days, the economics are as important as the art.”