The twisted, rusting hunks of steel that rested on the flat bed of a semi truck on Broadway in downtown Denver served as a solemn reminder to Coloradans of the terrorist attacks that shook this country 15 years ago.

One woman dabbed at her eyes with a tissue Sunday after looking at the rubble from the World Trade Center buildings destroyed by the attack in New York City on Sept. 11, 2001.

Others offered their thanks to the members of the armed forces who stood guarding the rubble, which was draped with a large American flag. A banner hung from the truck’s bed that showed a picture of the New York City skyline, minus the Twin Towers, with the words “Lost but not forgotten” printed on it. A Colorado flag hung over the pieces of steel, suspended from the ladder of a Lamar Fire Department truck. Other military and emergency vehicles were parked nearby.

“It’s pretty sobering, definitely,” said Maureen Garretson, an Arvada resident who sat on a bench near the temporary exhibit. “It makes me sad to think our country was attacked the way it was. It’s important to always have some sort of a remembrance of that day and hope we never have anything like it again.”

Colorado paid tribute to the nearly 3,000 people who died and the nearly 7,000 who were injured in the terrorist attacks committed on Sept. 11, 2001. The city of Denver and the state of Colorado marked the 15th anniversary of the attacks with a remembrance march, several speeches about unity and hope and performances by Big Head Todd and the Monsters and John Fogerty.

Before the musicians took the stage, the ceremony was somber and reflective.

Under the bright midday sun and in 90-degree heat, hundreds of members of various military groups, police officers, firefighters and other first responders marched from the Capitol to the west side of Civic Center Park. Crowds lined the march route, clapping and saying “Thank you” to the men and women in uniform.

After an invocation from two faith leaders, Gov. John Hickenlooper took the stage shortly after 1 p.m. and said Sunday was a day to pay tribute and to remember what happened in 2001.

“Fifteen years ago, our nation suffered the worst terrorist attack in its history,” Hickenlooper said, addressing a crowd of several hundred in Denver’s Civic Center Park. “We remember those we lost on September 11, 2001, in New York City, in a field in Pennsylvania and at the Pentagon. They were our loved ones, our family, our friends. We mourn those who perished on that fateful day and those who died protecting our freedoms every day since.”

Hickenlooper nodded to the families of men and women who died in the terrorist attacks and the families of those who have died in conflicts around the world protecting America’s freedom.

He said the presence of those families in Denver Sunday was a symbol of the strength of the nation. He asked members of the audience to show them their deepest sympathy and solidarity.

Colorado’s governor went on to discuss the continued threat of terrorism, 15 years after the 9/11 attacks.

“Sadly, there are those who continue to threaten our way of life,” Hickenlooper said. “We continue to witness attacks around the world from those who feel threatened by the expansion of freedom, democracy, justice. There are terrorist armies that continue to divide countries in the Middle East and Europe and across the globe. In the United States, attacks by self-proclaimed terrorists are becoming more common.”

He said Sunday’s ceremony was more than a remembrance of the past and a tribute to the fallen; it was also a tribute to the living and “all that we have learned about our nation and our collective humanity.”

“In the darkest moments, we witness true compassion,” he said. “We witness courage and extraordinary heroism from ordinary men and women. The actions on that day exemplify the best in what America and our great nation represents.”

Denver Mayor Michael Hancock asked the crowd to recognize and thank members of the armed forces “who serve and protect all of us around the world,” as well as the people who work in public safety in Colorado.

“September 11, 2001, changed all of us forever,” Hancock said. “Gathering here today is a testament to our resiliency and our strength. Our common belief in freedom and democracy unites us now as it did after 9/11. And we will continue to stand together in the face of adversity.”

Hancock said the will to prevail following the terrorist attacks 15 years ago is best signified by the Callery pear tree that endured the attacks.

The tree, which came to be known as the “Survivor Tree,” was discovered at Ground Zero with snapped roots, burned branches and other damage. The tree was removed from the site and rehabilitated by the New York City Department of Parks and Recreation. Eventually, the tree was returned to 9/11 memorial, where new branches began to grow.

“Just like that tree, Colorado remembers 9/11 and represents our nation’s resolve then and now,” Hancock said.

He motioned to the steel on display from the World Trade Center and said the relics were an “important symbol” of the lives lost that day 15 years ago.

“These are sacred artifacts,” Hancock said. “They also represent a stark reminder to Colorado, to Denver, to all of us of our obligation to work together to keep our community safe and secure.”

On the day of remembrance, it appears that Colorado’s elected officials set aside their political differences and joined together in a bipartisan coalition to reflect and honor those who lost their lives.

U.S. Sen. Michael Bennet, a Democrat, and his Republican colleague U.S. Sen. Cory Gardner took the stage together. Bennet remarked on the special role that Colorado played in the aftermath of the 9/11 attacks by sending first responders to New York and Washington to join in search and rescue efforts.

“It is so important for us to pay our respects to those lost on 9/11, and we also need to honor our soldiers who serve our country and the state of Colorado each and every day,” Bennet said. “Our brave men and women are still on the front lines, keeping our country and our values safe. They include thousands of Coloradans serving across the globe. They are all of us – our families, our neighbors. Their valor and commitment is awe-inspiring to us and we owe them a debt that can never be repaid.”

Bennet then introduced Gardner as his friend and colleague.

Gardner recalled being on an airplane during the attacks 15 years ago. He said he would never forget the moment the pilot told those flying on his airplane that there had been an attack on the World Trade Center.

“We all have our 9/11 stories and as we look back 15 years, it’s important to remember and recognize the first responders,” Gardner said. “They were and are the heroes of the day. We remember the first responders who continued in their rescue efforts as the towers collapsed around them, giving their lives to save countless others. Courageous men and women ran toward destruction, putting their own fears aside.”

Gardner said each new terrorist attack is accompanied by stories of people committing acts of bravery.

“We stood up for freedom, freedom as mighty as our Colorado rivers, freedom as free as the Colorado wild, freedom that we continue to fight and strive for today,” Gardner said.