The final steel beam was lifted by crane Monday to the top of SunTrust Park as Braves executives, dignitaries and media members watched from what will become the playing field of the new Cobb County stadium.

The 33-foot-long, 1,422-pound beam was bolted into position 155 feet above field level, completing a “topping-out” ceremony that Braves chairman and CEO Terry McGuirk called a “major milestone” in the building of the ballpark.

In keeping with construction-industry tradition, the final beam had a flag and a tree attached to it — in this case, an American flag and an ash tree.

Marc Dyer, senior project manager for Hirschfeld Industries, SunTrust Park’s steel fabricator, is a veteran of many topping-out ceremonies. Usually, he said, an evergreen tree is attached to the last and highest beam. But an ash tree was chosen this time, he said, because that is a wood from which baseball bats are made.

Dyer also offered a history lesson on topping-out ceremonies, noting there are numerous versions of why, when and where they started, all dating back many centuries.

In any case, the Braves’ ceremony signified that the $672 million stadium, while far from complete, has reached its ultimate height.

“I’m happy to report construction is on time and on budget,” said McGuirk, declaring again that the stadium and much of the adjacent mixed-use development will be open for the start of the 2017 season.

Among those in attendance for Monday morning’s ceremony were the five Cobb County commissioners and executives from SunTrust Banks, which signed a 25-year naming-rights deal with the Braves in September 2014.

“It has exceeded my expectations,” Jenner Wood, SunTrust’s corporate executive vice president, said of the stadium. “It’s going to be a great thing for us to have our name on this venue.”

As he looked around, Wood said he especially likes the coziness of the new ballpark.

“It is a park. It’s not a stadium,” he said. “It’s a park because it has a feeling of closeness.”

Already in place are the SunTrust Park sign atop the center-field video board, prominent signs for sponsors Coca-Cola and Delta, even pennants hanging from a right-field light pole. And there are 6,800 tons — or 13.6 million pounds — of structural steel, which McGuirk said “would be 50 miles long” if placed end to end.

The ceremonial final beam, which ultimately will support stadium lights, was signed by McGuirk, other team executives and dignitaries before it was hoisted to the top of the ballpark.

About nine months remain on the stadium’s 30-month construction schedule. Much work remains to be done, including the installation of 41,000 seats, the playing field (starting with its drainage and irrigation sub-surface) and all sorts of interior construction.

“We’ve known from the very beginning this was going to be a very aggressive schedule,” said Mike Plant, the Braves’ president of development. “We’ve also known we are playing our first game here in April of 2017. So there is not a grace period.”

The Braves’ front office is scheduled to move into its SunTrust Park offices in December, Plant said.

“By that time, a lot of the park will be ready to go,” he said.

On two issues of much concern to many Braves fans — how they’ll get to the new stadium and where they’ll park — Plant said the team will release a “transportation and parking update” in about two weeks.