A steel beam recovered from the rubble of the World Trade Center kicked off its national tour Saturday as part of an emotional commemoration for the heroes who made the “ultimate sacrifice.”

The coast-to-coast tour by the Tunnel to Towers Foundation was launched ahead of the 25th anniversary of the 2001 terror attack, in part to help enlighten kids who weren’t alive at the time.

The commemoration was dreamed up by Tunnel to Towers Foundation CEO Frank Siller as a way to honor his fallen FDNY brother Stephen, who raced to the WTC from Red Hook through the Brooklyn-Battery Tunnel on Sept. 11, 2001.

“This steel is so significant because it has the soul of my brother in it, and the souls of so many,” said Siller.

“It’s important to recognize the heroism that was exhibited on that fateful day. It was nothing short of incredible. As we reflect on 25 years that have passed since September 11th, 2001, we must remember the extraordinary sacrifices of ordinary people who gave their lives and in doing so, became heroes.”

The “sacred artifact” is a 26-foot-long, 16,000-pound steel beam recovered from the rubble of the South Tower.

It was officially unveiled Saturday in an emotional ceremony just steps away from the World Trade Center — where it will return Sept. 11 for the 25th anniversary of the terror attacks.

The steel — traveling in a box truck — then moved onto its first official stop in Fort Wadsworth on Staten Island, where the foundation will host supporters for a kick-off BBQ.

The hallowed item will make more than 35 stops at major landmarks across the country, including the Mt. Rushmore National Memorial, the USS Arizona Memorial Gardens and the Space Center Houston as the tour covers more than 10,500 miles, the foundation said.

A major goal of the tour is to educate America’s youth, who might be too young to comprehend the sacrifice and heartbreak that the tragedy wrought before they were born.

“People are not going to experience in their life to touch a piece of steel that was part of one of the towers that came down. It is an experience that later on in life they will explain to their children or grandchildren and so on and so forth that they were able to be there for the 25th to honor in their small way,” Siller previously told The Post.