Three-hundred feet above Atlanta United’s pitch, a horn blared Wednesday afternoon, eight giant “petals” weighing 500 tons each slid quietly on long tracks—slowly at first, then up to 90 feet per minute—and a jagged, growing oval shined below.

A cool breeze cut the coliseum’s sweltering, off-limits upper regions. A growing skyline was unveiled. And about eight minutes later—four minutes faster than engineers and architects had always predicted—the Mercedes-Benz Stadium roof was fully open, the crowning, albeit delayed achievement of a $1.5 billion project a half-decade in the making

“It’s absolutely no exaggeration to say this is far and away the most complex, intricate, and interesting roof put on a sports complex anywhere in the world,” the stadium project’s senior director, Mike Egan, asserted from a perch suddenly in the sunshine.

Added Steve Cannon, CEO of AMB Group, the Atlanta Falcons’s parent company: “We’ve got the most unique roof structure in the world, and it is fully functioning to design specifications. This architectural icon … is coming online, as of today.”

Eleven months, 2.5 million guests, 54 ticketed events, a few water leaks, and one College Football National Championship since the stadium opened, the marvel that is the aperture-like roof has been turned over to MBS brass, and it’ll open and close at the push of a single button in a downstairs control room, near the press box.

Officials on Wednesday led media up a mountain of metal stairs, across harrowing catwalks, and to the base of the great mechanism for a firsthand glimpse of the roof in action. A stadium roof in China opens in a similar way, Egan said, but nothing is of comparable scale.

Have a glimpse below of up-close footage and photos of the roof in action—allowing a skyline vantage like nowhere else in the city.

But first, the million-dollar question: What took so long?

“We came to realize last summer that the [weight of the petals] had to be equally balanced across the two [supporting] rails, otherwise it creates drag that would burn out the propulsion system prematurely, which is designed to last 30 years,” Egan explained, in the best layman’s terms he could muster.

“We knew exactly what we needed to do—we just ran out of time before it was time to actually open the building,” he continued. “The roof has always worked ... it was just a question of we didn’t want to run it frequently, because of the drag. People thought the roof was broken ... or had design issues. That was never the question.”

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The Benz, in retrospect

Crucial moments in the creation of Atlanta’s most impressive sporting venue:

• June 2013: Early stadium designs emerge, with one 360 Architecture official opining: “I think it’s going to set the bar.”
• Late 2013: The 18-acre “south site” is chosen for the stadium, versus a location in Midtown off Northside Drive.

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• July 2014: The oldest African-American Baptist church in Atlanta—Friendship Baptist, established after the Civil War in 1866—is demolished to make way for the stadium. Historic Mount Vernon Baptist Church was also razed.
• May 2014: About 500 invited guests join Falcons owner Arthur Blank, then-Mayor Kasim Reed, and NFL commissioner Roger Goodell for an explosive groundbreaking ceremony at the site.

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• June 2015: News emerges that Atlanta’s MLS expansion team will be named “Atlanta United FC”—a club that would smash league attendance records once The Benz opened for play.
• August 2015: A 27-year naming rights deal christening “Mercedes-Benz Stadium” is announced.

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• April 2017: Lingering construction complications, primarily hinging on the complex roof, push the stadium’s opening back to a Falcons preseason matchup in August.
• September: The stadium debuts as an NFL facility with the roof open for a Sunday night contest between the Falcons and Packers—the first open-air Dirty Birds game in Atlanta since 1991.
• December: A second round of explosions implodes the Georgia Dome completely.

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• May: The Falcons’s parent company, AMB Group, declares the final kinks are being worked out, and the roof will soon function as intended, opening and closing within 12 minutes.
• July 25: The Benz hosts a ceremony to showcase the now-functioning roof’s opening and closing capabilities.
• July 29: On Sunday at noon, the Atlanta Falcons will host an open practice. Before the team hits the turf, however, attendees will have another chance to witness the roof opening and closing. Stadium officials say some 50,000 people are expected to show up.