Tens of thousands of people crammed into downtown Montreal on Thursday night to throw a giant homecoming party for local band and global success story Arcade Fire.

The critically acclaimed rockers capped off their world tour with a free outdoor show as a way to pay homage to their city.

"Merci beaucoup, Montreal!" frontman Win Butler shouted into the microphone after his band had the massive crowd bouncing throughout the aptly titled opener, Ready to Start.

"Our hearts are very full, thank you. Alright, are you guys ready?"

Organizers expected at least 75,000 people to swarm a new open-air venue, Place des Festivals, for the band's triumphant return after a year on the road. By the time the eight-person group opened the show, the huge mass of people had formed in front of the stage and pressed together shoulder to shoulder.

Renowned for its energetic live performances, Arcade Fire swept album-of-the-year accolades at this year's Grammy, Juno and Brit Awards for their third album, The Suburbs. The album was a chart-topper in Canada, the U.S. and the U.K., and it also won this month's Polaris Music Prize.

After the curtain raiser, Arcade Fire launched into Keep the Car Running and then No Cars Go, both from their second album, Neon Bible. Thursday happened to be Car Free Day in Montreal, where parts of the core was closed off to automobiles.

"Happy no cars day," Butler said before No Cars Go, drawing cheers from the crowd.

The party was a homecoming in more ways than one. Eight years ago, organizers of a small local festival helped promote the band's debut album at a Salvation Army. On Thursday night the band was repaying the favour with the monster gig that helped kick off the 10th edition of that same annual event — the POP Montreal music festival.

"It just feels so perfect tonight," Butler said. "It really feels like home, thank you so much for supporting us."

Grammy preceded a string of wins

Thursday's performance came seven months after Arcade Fire stunned the music world by taking home the coveted album of the year prize at the Grammy Awards. Even Butler expressed shock at the time. When the award was announced in February, he dropped to his knees and said, "What the hell?" before delivering a shout-out to the group's hometown.

''Everyone kind of had a sense that they were a special band...You kind of knew early on that they had a lot of potential' —Dan Seligman, POP Montreal

"I just want to say thank you, merci, to Montreal, Quebec, for taking us and giving us a home and a place to be in a band," said Butler, who grew up in Texas.

Still stunned, Butler then swore before adding: "I can't believe it, we won. Merci Montreal!"

The band followed up the Grammy by winning prizes at the Junos and the Brits — including album of the year at each. But the group expressed relief at a paid show Wednesday night to be back home after a long run on the road. While the group members' hometowns span across the continent, Montreal was where they came together and grew as a band.

When Arcade Fire played international music festival POP Montreal in 2003, the group had already developed into a popular attraction at tiny venues around the city, the festival's creative director recalled.

"Everyone kind of had a sense that they were a special band," said Dan Seligman, a longtime friend of the group. "You kind of knew early on that they had a lot of potential."  

He recalled how POP Montreal promoted the launch of their first album, Funeral, at a Salvation Army in Montreal. Seligman said reviews from that record put them on the map as an important band in North America and Europe. But he said despite the group's commercial success, the band members haven't changed much and they still prefer the intimacy of putting on smaller shows.

"I think at heart they still kind of crave for that underground feeling of playing in front of like 100 people," he said of Arcade Fire, which performed Wednesday in front of a couple of thousand fans for a paid show at Montreal's Metropolis club.

Fundraising for Haiti

Arcade Fire used Thursday's concert to raise funds for KANPE, a non-profit organization devoted to Haiti. The band offered VIP passes to the first 100 fans who donated at least $200 to the charity.

The concert also marked the French release of the book Mountains Beyond Mountains, a work by author Tracy Kidder on the life of Dr. Paul Farmer, co-founder of the Haitian non-profit organization Partners In Health. The book was a source of inspiration for band members and one of the tracks on the The Suburbs is titled, Sprawl II (Mountains Beyond Mountains).

In the hours before Thursday's show band member Régine Chassagne, whose parents come from Haiti, was scheduled to speak at two universities with Farmer about humanitarian engagements in the impoverished nation. Chassagne, who's married to Butler, brought Farmer on stage in the middle of the concert to introduce him to the fans.

"The book really changed my life," she told the crowd.

Speaking in French, the American physician thanked Montreal and Quebec for helping Haitians. Butler challenged Quebecers to continue their support of Haiti, which is still struggling to recover after the devastating January 2010 earthquake.

"I really believe that Montreal and Quebec are really going to transform Haiti," he said from the stage before firing into the tune Modern Man.

"The City of Montreal is just so committed to Haiti that I really believe that it's possible."

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A massive crowd gathered for the free outdoor Arcade Fire concert in Montreal Thursday. (Graham Hughes/Canadian Press)