People came from across the country for the 9/11 Memorial Stair Climb.
Nearly 3,000 people climbed 110 stories at Lambeau Field in memory of the 343 firefighters who lost their lives on September 11, 2001.
Pierce Manufacturing and the Green Bay Metro Fire Department hosted the 6th annual event.
They said this is one of the biggest events of its kind in the nation.
Each climber received a badge with the name and photo of a firefighter who was killed trying to save others during 9/11.
The 110 stories they climb is equivalent to the 110 stories in the World Trade Center.
Many firefighters climbing wore full gear and an air pack.
"You see them carrying flags. You see them with their families. Kids are with them. I just think that the significance of that is they know how terribly important this is to remember and to support families who have lost loved ones," said Fire Chief David Litton of the Green Bay Metro Fire Department.
Some told us they're climbing to remember the 343 fallen firefighters from 9/11, but they're also remembering the firefighters in their own communities who put their lives on the line every day.
All proceeds go to the National Fallen Firefighters Foundation to support the families of firefighters who sacrificed their lives to save others.