DENVER - It's a tradition that started in downtown Denver: each year on the anniversary of 9/11, firefighters all over the country climb up the stairs of buildings to remember the firefighters who lost their lives in the twin towers.
On Sunday, five years after the first event that included just a few firefighters, 343 firefighters from around Colorado climbed the Centurylink building downtown - the same number of firefighters who died while doing their jobs after the attacks in New York City.
That climb in Denver is 55 flights of stairs, just half of the World Trade Center towers. And so the firefighters made the trip twice.
"We actually knew some of the firefighters that were killed that day," said David McGrail, district chief with Denver Fire Department. McGrail was one of the original firefighters who put together the walk.
Every participant carries a photo of one of the firefighters who passed.
The stair climb started in Denver in 2006, and now multiple climbs are offered throughout the metro area.
It's such a popular event that the registration for firefighters who wanted to get involved filled up in one hour.
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