The 72-story climb was held at 4 World Trade Center.
"Good cause. ... Never forget that these guys gave the ultimate sacrifice," one firefighter from Coral Gables, Florida, told WCBS 880's Peter Haskell.
The morning started with a moment of silence at the 9/11 Memorial. Then the 343 firefighters began their climb.
The number of participants matched the number of FDNY members killed on 9/11. Photos of each of them lined the stairwell at 4 World Trade Center on Sunday.
Sweaty and spent, finishers were greeted at the top.
The event was started by firefighters Chris Barber and John Mills.
"Personally, I lost my father in the South Tower, so obviously he runs through my head," Mills said.
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