Thousands of runners and walkers took part in a 5K run Sunday to honor first responders.

The Tunnels to Towers 5K kicked off at the Brooklyn side of the Hugh L. Carey Tunnel, which was formerly known as the Brooklyn Battery Tunnel.

The 5K retraced the final steps of Stephen Siller, a New York City firefighter who lost his life on 9/11 after strapping on gear while running through the tunnel to the Twin Towers.

The event also honored other first responders like firefighters, law enforcement, and the thousands of others who died on 9/11.

The 3.5 mile event ends in Manhattan.

The event helped to raise funds for the Fallen First Responder Program, which helps families pay off mortgages on their homes or set up trusts for their children to help with education.