It showed up Tuesday night, 12 hours before the big test.

A masked crew received the white-coated, roughly 30-foot-long beam at the corner of Liberty Drive and Fan Pier Boulevard. A product of Canada, the hunk of iron spent its first night in Boston just feet from the harbor.

Around 8 a.m., a crane lifted the beam 17 stories above the ground alongside pieces nearly twice its size.

“We always want to make sure everything fits perfectly, so you don’t get it up there and go, ‘this is half-an inch short,’” said Richard Martini, executive managing director of the Fallon Company.

It fit.

The long-awaited piece topping off MassMutual’s office structure marked not only a step toward the company’s expansion into Boston but a feat for a construction team that welded, poured concrete and fireproofed steel under the threat of COVID-19. The project marked a first for even the most seasoned tradespeople — their first build during a pandemic.

“It’s a little weird with the masks and stuff, but other than that it’s just like every other day,” said Sean Clerkin, 32, a Boston native who was part of the raising gang on the construction site.

While COVID-19 has shaken up the local economy, MassMutual’s presence in Boston’s Seaport District continues to take shape after plans 15 years in the making. The Turner Construction Company crews were sidelined for nine weeks as Boston construction sites and businesses across Massachusetts shut down to reduce the spread of the virus.

Since returning to the site, construction workers have made up much of the work. As of Wednesday, they were roughly a month behind. Crews were fireproofing some of the iron beams before the “topping off” ceremony began, preparing the building for the installation of the stainless steel facade that will eventually encase the curvy building.

“These workers have done a superb job,” said MassMutual CEO Roger Crandall. “We’re still optimistic we’re going to open in the fall of next year and super optimistic we’ll have a vaccine and we’ll actually be able to have everybody at the office."

Roger Crandall - Boston

MassMutual CEO Roger Crandall signs the last iron beam before it is lifted up 17 stories to the top of the company's Boston building, which is expected to open in fall 2021.

When the doors open, the steel beam covered in autographs will be completely out of view. The 17-story tower will host 1,000 MassMutual employees and the startup accelerator MassChallenge. Employees will walk in and out of the building freely and enjoy the outdoor plaza facing the Fan Pier Marina.

On Wednesday morning, though, all eyes were on the white iron beam being christened signatures, stickers and messages. A small, bare evergreen tree stood fixed on the beam. The tree fitting is a tradition dating back to 8th century Scandinavia that symbolizes health and prosperity. The tradition has survived centuries of global power shifts, world wars, industrial revolutions and a recession sparked by a pandemic.

“Topping off is to honor the workers; not investors,” one person wrote in red marker.

Crew workers and company executives grabbed markers from the table on the right, usually returning to the table for hand sanitizer.

“It’s a big deal because it’s a tradition,” said Jessica Devance, a second-year apprentice in the Iron Workers Local 7 Union. “We helped put up that building.”

Devance was hired two weeks before the city shut down workplaces due to COVID-19. When the construction site reopened, she and her colleagues helped with tack welds that hold metal in place, water runs, equipment sanitization and other tasks to get the project back on schedule — or as close to it as possible

Clerkin, the journeyman on the raising gang, signed his name and saw the beam through the rest of its journey. For him, the whole affair was business as usual.

“Just means another job done,” he said.

The beam carriers dozens of other names with him, including Crandall, Boston Mayor Marty Walsh and the Haugh brothers.

Joe Haugh signed his name and slapped a memorial card of his brother, Paul Haugh. Paul, an ironworker and a combat veteran who served in Afghanistan for the Marines, died Feb. 14, 2019, in a motor vehicle crash, according to his obituary. He was 28 years old. “RIP Paul” and “RIP the Sarge” popped up in other parts of the beam.

The beam encountered one more test before Crandall, Walsh and other dignitaries took the stage at the edge of the site: a balance check. The workers lifted it a few feet, and again, it passed. The workers gathered round for pictures of the guest of honor.

“Boston Strong — people say it, but this is an example of seeing it,” Crandall said of the construction work as the “topping off” ceremony began, his first.

After his remarks, even Crandall couldn’t help but stare up at the beam as it made its slow ascent to the Seaport’s skyline.

See story on masslive.com.