The women’s final of the U.S. Open will be played that afternoon.

New York Fashion Week will be in full swing.

The Golden Lion will be awarded at the Venice Film Festival.

Hollywood will count the opening weekend for "Practical Magic 2."

And, because apparently every date requires a commercial sponsor, it will be "National Chocolate Milkshake Day."

Why do marketers and brand managers embrace Sept. 12?

Yes, it marks the unofficial beginning of fall. The weather starts to change. Children return to school. New television shows, movies, clothes, phones and political campaigns arrive with the promise of a fresh start.

But that is not the real reason.

Sept. 12 means we can put Sept. 11 in the rearview mirror for another year.

For many, the question still produces an exact answer. A room. A street corner. A classroom. A television screen. A phone call that would not go through. But each year, fewer people can answer it from memory. For an entire generation, 9/11 is something they learned about in school.

That makes the question more urgent, not less. What exactly are we remembering? What did we believe America was defending that day? And 25 years later, who do we believe has the right to call themselves an American?

Here is my story.

On Sept. 11, 2001, I stood on the roof deck of my company's building, looking downtown at the smoke and flames. Firefighters, police officers and ambulance crews acted with a selfless bravery that still defies explanation. I remain humbled by their unflinching efforts to save people trapped inside those terminally wounded towers.

I am a documentary filmmaker. Almost without hesitation, I knew what I had to do. I had to capture what was happening in my city.

Historians have the benefit of time. They can examine evidence, piece together facts and search for truth in the details. On 9/11, we had no such luxury. We had to record the images, stories and details as they unfolded, or risk losing them forever.

I began collecting footage shot by professional filmmakers and ordinary New Yorkers who had picked up their cameras that morning. Their images captured more than the attacks. They recorded the fear, confusion, anger, grief and extraordinary solidarity that followed.

The week after the attacks, people were numb. The images of the planes hitting the towers, the buildings burning and then falling, were seared into our minds. As the city mourned and began the long work of recovery, I tried to contribute with the tools and skills I had. There was a story that needed to be told.

So I made a film. It's called "7 Days in September."

The footage did not belong only to me or to the people who shot it. It became part of the historical record. The CameraPlanet Archive was donated to the New York Public Library, where those images and voices will be preserved and made available to future generations.

In the weeks after 9/11, New York proved itself to be a truly global community. People from every neighborhood, nationality, religion and economic class came together. Volunteers filled the streets. Restaurants fed rescue workers. Families searched hospitals. Strangers stood in line to donate blood. The cleanup began.

Later, an open call for memorial concepts brought forward a young Israeli American architect named Michael Arad. His beautiful and meditative design, "Reflecting Absence," was selected for the site. Today, the names of 2,983 people killed in the attacks of Sept. 11, 2001, and the the six killed in the 1993 World Trade Center bombing are etched in bronze around its two enormous pools.

But how many of those people would be welcomed into the United States today?

How many would satisfy our current political tests for who belongs here? How many would be considered “real” Americans?

The people killed on Sept. 11 came from more than 90 nations. Among them were hundreds of foreign nationals and an unknown number of undocumented immigrants. They were delivery workers, waiters, cleaners, cooks and construction workers. Some lived so far outside the official system that, after they disappeared, their families struggled to prove they had ever been inside the towers.

Its volunteers answered phones and accompanied relatives on grim journeys through the city. Fear of immigration authorities complicated everything. Some friends and relatives were afraid to provide information, even when someone they loved was missing.

Their immigration status did not make their deaths less real. It did not make their families’ grief less profound. It did not make their work less valuable or their place in New York less legitimate.

The attacks killed 2,977 people, but that number alone does not capture what was lost. New York was attacked precisely because it represented something larger than itself: an open, complicated, imperfect city built by people who came from everywhere.

Twenty-five years later, we are again asking painful questions about American democracy. What are we fighting for? Who belongs? Who gets protected? Who gets expelled, erased or treated as less American than someone else?

On Sept. 11th, we will remember the towers, the people who died and the rescuers who ran toward danger. We should also remember the pride with which we once defended our shared values and the remarkable collection of immigrants from around the world who helped build this country.

On Sept. 12, we will order new phones, watch tennis, argue about politics and move on. That is what people do. It is what cities do. It is even what nations must do.

But before Sept. 11 recedes again, we should remember not only how nearly 3,000 people died, but how millions of people responded. For a brief moment, New York understood that its strength came from every language, nationality, religion and neighborhood gathered on the same small island.

America is a nation of immigrants. That was true on Sept. 10, 2001. It was true when people from more than 90 countries died the following morning. And it will still be true on Sept. 12, 2026, whether our politics acknowledges it or not.