DENVER (CBS4)– Thousands of people gathered to honor 9/11 victims and firefighters at the Red Rocks Stair Climb on Tuesday for the 9/11 memorial. It’s been 17 years since the attacks on the World Trade Center and Pentagon.

(credit: CBS)

Participants will march nine laps around the naturally-occurring amphitheater which equals 110 stories of the World Trade Center in New York City.

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(credit: CBS)

The stair climb honors the 343 FDNY firefighters who lost their lives in the attacks.

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Dozens of fire departments from across Colorado are expected to take part in the climb.

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(credit: CBS)

The 9/11 Red Rocks Stair Climb is one of the biggest such events in the country. The climb benefits the FDNY Counseling Services Unit and the programs provided by the National Fallen Firefighters Foundation to support their families.