The deadliest terror attack on American soil happened today, fifteen years ago.

Nearly 3,000 people died.

More than 400 of those were first responders.

Sioux Falls Fire and Rescue honored those who lost their lives in the line of duty.

A Remembrance and Fallen Firefighter Memorial was held at the stations headquarters.

Along with a bell ceremony and a presentation of colors, video and images were played as a tribute to what all first responders went through on September 11, 2001.

"It's an important thing for people to remember the magnitude that happened on that day, to remember that our freedoms are not free, not to take that for granted, and not to take our loved ones and our way of life for granted,” says Sioux Falls Fire and Rescue firefighter Jon Sanders.

A big crowd attended Sunday night's memorial.

All the seats were taken, leaving standing room only.

The Battalion Chief says seeing this is what keeps him going on tough days like today.

"I am very honored to serve, first and foremost to the citizens of Sioux Falls, but also in the fire service profession,” says Chief Michael Clauson. “It's very rewarding and it's the least I can do to give back to all the men and women that have come before us. For me, it's just deep seeded in my heart.”

This is the 29th Minnehaha County Fallen Firefighter Memorial Service.