Firefighters from around the region each wearing more than 30 pounds of gear were among the tens of thousands of runners who on Sunday retraced the steps of Stephen Siller, an FDNY member who sprinted through the Brooklyn Battery Tunnel toward Ground Zero on the morning of the 9/11 terror attacks and ultimately lost his life.

"You had the chills the whole time, thinking of his story," said Jen Hawker, 36, of the Scranton, Pennsylvania, fire department. She wore heat-resistant "bunker" pants, jacket and a helmet, and noted that Siller, 34, had run through the tunnel in dramatically different circumstances 13 years ago.

"I couldn't believe he did this. . . . I couldn't imagine the chaos of people running past. I couldn't imagine the panic," she said.

Siller's family has for 13 years hosted the annual Tunnel to Towers 5k Run and Walk in his memory. More than 35,000 participants ran or walked through the tunnel from Brooklyn to lower Manhattan Sunday morning, including police officers, military cadets and student athletes.

FDNY members in dress uniforms holding banners with photos of colleagues lost in the terror attacks greeted runners on their way out of the tunnel. Siller, 34, raised in Rockville Centre, was an FDNY firefighter off-duty Sept. 11, 2001, when news came across his scanner of the attack on the World Trade Center.

He had been headed home to Staten Island and turned his car around immediately. When he learned vehicles were being blocked from entering the tunnel, Siller strapped on 60 pounds of gear and ran along the tunnel's catwalk to Manhattan. Siller and the members of his squad, Company 1 of Park Slope, Brooklyn, did not survive the attacks.

Allison Kane, 33, of Stony Brook, a teacher who was among 50 supporters of the Suffolk Police Running Club participating in the event, said she was glad to back the Sillers' foundation because it honors all the men and women who lost their lives on Sept. 11. She remembered the horror of not being able to reach her sister on the day of the attacks.

"It's the American spirit," Kane said of why the event still turns out large numbers. "It's the resiliency of Americans."

Lt. Sean Hardy, 24, of Smithtown, who ran with his Smithtown Fire Department colleagues for the second year, said it was very emotional to see the FDNY members lined up with photos of the fallen.

Kody Schrum, 24, of Mill Basin, Brooklyn, a former Marine and Nebraska native, is new to the FDNY. He wore what he estimated was 45 pounds of firefighting gear for the run.

"I wanted to replicate what he did on 9/11," Schrum said. "It was definitely an eye-opener."

FDNY Commissioner Daniel Nigro, at a festival held afterward in the shadow of the newly erected 1 World Trade Center, said the Sillers have turned Stephen's loss into a victory.

"The victory gets greater each and every year," Nigro said.

The foundation has raised more than $35 million the past 13 years for such initiatives as building homes for returning military members.