New York (AFP) - In one Brooklyn firehouse, there is only one survivor of the September attacks still active, but the memory of 12 "brothers" lost in the twisted and smoking debris of the World Trade Center is still achingly alive.

The words "We will never forget" now appear on a metal plaque affixed to the facade of the Squad Co. 1 firehouse in Brooklyn's fashionable Park Slope neighborhood. The names of the 12 firefighters from the unit who died that day are inscribed there as well.

Their retired colleagues, family members and active firefighters gathered around an American flag on Saturday -- as they do every September 11 -- for a more intimate ceremony than the pomp-filled televised event in Manhattan attended by President Joe Biden and former presidents Barack Obama and Bill Clinton.

"I'm the last guy, yeah, that worked with these guys," 54-year-old Paul Stallone said on the sidewalk outside the fire station just before the dark-clad gathering observed a minute of silence (8:46 am, or 1246 GMT) to mark the moment a plane hijacked by Al-Qaeda militants struck the first World Trade Center tower. 

"Some of the pain is, is coming back," Stallone said, adding that there was also a sense of "joy to see the families and how they moved on."

For two decades, Stallone -- who as a child arrived in Brooklyn on September 12, 1976 with his immigrant family from Italy's Puglia region -- has lived with feelings of survivor's guilt.

The only reason his name does not appear on the front of the fire station, on one of the squad's firetrucks or on the T-shirts being worn Saturday, is that he had just completed a shift late the day before.

They 'didn't come home'

"When the towers got hit, I was home and came back to the firehouse," he said. "And that's what saved my life, because I grabbed my gear and by the time I got to the city, the towers came down."

"The guys that came in that night, didn't come home. The guys that came in that morning, didn’t come home," he said, struggling to contain his emotions.

Among his 12 lost "brothers" was Stephen Siller, a 34-year-old father of five. Siller was just coming off an overnight shift when word came of the attack. 

When his firetruck was unable to make it through the tunnel linking Brooklyn to Manhattan, Siller jumped out and -- with 60 pounds (27 kilograms) of equipment on his back -- began running toward the attack site.

He did not come back.

His older brother Frank Siller wanted to mark the anniversary in a meaningful way.

He set off last month on a 500-mile (800-kilometer) hike from Washington to Shanksville, Pennsylvania -- where another hijacked plane crashed that day -- and finally to New York, finishing by passing through the same tunnel his brother had used, all to raise money for his Tunnel to Towers foundation, which supports victims' families.

"I miss my brother so much," he said. "Even though it's 20 years later, you never get over something like this. You learn to live with it."

343 lost firefighters

As the magnitude of the attack in New York became clear, firefighting units from throughout the area quickly converged around the World Trade Center. In all, 343 firefighters -- from 78 fire companies, some coming from Queens or the Bronx, were lost.

The ceremony Saturday at Squad Co. 1 was followed by a memorial mass at a neighborhood church, but also by a reunion of the families whose lives were uprooted -- but also brought closer together -- on September 11. People chatted quietly, sharing family news or catching up on each others' lives against the  crackling in the background of walkie-talkies. 

Theresa Johnson, a cousin of Matthew Garvey -- who died that day, aged 37 -- said she still feels "anxious."

"My heart hurts," said Johnson, who was dressed all in black. 

"It's a day where I feel anxious, because 20 years later, we're still in a situation where we have these terrorist attacks in Afghanistan.

"It’s still here," she said, speaking under a crystal blue sky very much like the one on the fateful day 20 years earlier.