Twenty years after the tragic events of 9/11, it’s hard to imagine any person who doesn’t have an image (or several images) of the Twin Towers, whether on fire or collapsing, or the panic of people running around them.

But there were other events of the day. The crash at the Pentagon; the hole United Airlines Flight 93 created in a field in Somerset County, Pennsylvania.

And, of course, all the individual stories of escape, survival, bravery, and sacrifice.

For older viewers, 9/11 was a reality, but for Gen Z, those stories are just stories — not memories at all.

9/11: One Day in America, a new six-part docuseries, which premiered at Tribeca Festival, is launching just ahead of the milestone anniversary (on August 29) on National Geographic.

The filmmakers knew that they had to be “unflinching but respectful,” as producer Caroline Marsden puts it, in the archival footage they selected to include (and exclude), as well as the tales they chose to have recounted (or not)

The docuseries, produced in conjunction with The 9/11 Memorial and Museum, doesn’t skimp on repeat images of American Airlines Flight 11 or United Airlines Flight 175 crashing into the towers.

Nor does it skip close-up helicopter shots of people trapped on upper floors waving out the windows for help or jumping — images that are disturbing and potentially re-traumatizing for those who lived through the day.

But Marsden feels it is to those survivors’ benefit that such images keep being shared: “When we’re looking at footage of people waving from the top of the tower, we had to make sure that those people were not identifiable. But I think in making it unflinching, it was respectful also to the people who we interview because a lot of them are talking about struggling with suicidal thoughts 20 years later, and I think you don’t fully appreciate why that is unless you understand what they went through — unless you understand the horror of what they witnessed,” she explains.

9/11: One Day in America is solely focused on those survivors, forgoing celebrity voiceover in favor of making sure “the only voices you would ever hear would be people there on the day,” Marsden continues. But it was also intentional to leave out the celebrity politicians of the moment, such as then-mayor (and now disgraced lawyer) Rudy Giuliani or then-President George W. Bush.

“We didn’t want anything to distract, and I think the people who survived that day, their narratives have been hijacked by the politics of it in many ways. And so, we wanted to strip all that down and just get back to the the testimony,” Marsden says. “I think no matter what George Bush says, his very presence is political.”

Still, executive producer Dan Lindsay adds, “The intention was to as wide of a spectrum of experiences of that day as possible and not just focus in particular on a certain group like first responders or a particular story in the building. So, there was an intention of a diversity of people and experiences and then also, there was an intention behind the idea of, ‘Could we find stories that interconnect in a way?’”

Over the six episodes, the docuseries includes such first responders as Joseph Pfeifer, the first FDNY chief to respond to the call for help down at the World Trade Center who lost his brother that day, and Heather “Lucky” Penney of the United States Armed Forces, who took to the sky to stop any other planes being used as weapons.

But it also includes everyday people who acted as heroes, including Jason Thomas, a former marine, and Chuck Sereika, a former EMT, who both went down to the pile to search for survivors and helped rescue Port Authority police officers Will Jimeno and John McLoughlin.

It also features Ron Clifford, who was only going to the World Trade Center that fateful day for a meeting but ended up helping burn victim Jennieann Maffeo. (Maffeo died from her injuries in October 2001.)

Some of these names sound familiar, because theyGuided by this philosophy, are people who have told their stories before. But because the filmmakers were working towards this release on such an important anniversary year, “We certainly didn’t want to out-rule anybody because they’d previously told their story,” Marsden says. She credits executive producer David Glover with saying they just needed to make “an epic version of this that just has all of those stories and brings them all together.”

Guided by this philosophy, the narrative structure of “9/11: One Day in America” was born. Each episode features multiple interviews from people who shared the same intimate experience on the backdrop of this larger day. They tell their stories individually, but it is their shared account that shapes the bigger picture.

Director Daniel Bogado told each subject to take a full day off for their interviews. He sat with them for hours so they could tell their uninterrupted stories, some of which, he notes, when told from start to finish, “were two hours long” on their own. His approach was to keep them “in the moment” as much as possible.

“We tried to be immersive and present day. On that first go, a fresh emotion comes through,” he explains. “They were gracious and welcoming for us; they were enthusiastic contributors and wanting to participate. And I think that helped set the tone, which was, this is not like any other documentary where we just need to say A, B and C — the story points — and then we go. We wanted to achieve something a bit more profound than that.”

Adds Marsden: “The way we’re filming it is right down the lens so you have a very intimate feel to them.”

Most of the stories are hopeful, choosing to focus on acts of courage, even when the outcome isn’t all that positive. The docuseries does not really discuss long-term health effects of the day, despite many of the contributors living with them.

But Bogado didn’t want to shy away from the full truth of the day, which he calls “the best and the worst of humanity.” While most of the worst came from the terrorist attacks themselves, there are a few other stories sprinkled in about individuals who chose not to help, likely out of fear, and saved only themselves when the opportunity arose.

“As a documentary maker your first commitment has to be to the truth,” he says. “And so, the original pitch indeed was, ‘This will be a series that will show the the worst of humanity and also the best of humanity.’ In just doing very deep research, we really became familiarized with as many many loving stories as we could. It became very clear that the stories of solidarity and heroism and bravery, courage and kindness that you see many of which highlighted in the series, they are not an exception. They were not difficult to find. We had to find a balance because I was not interested in making a series that was just a catalogue of horrors because I thought that would be very difficult to watch.”

Another important area to balance was how much of the events in New York to show, versus what was happening in Washington, D.C. or on the ground in Pennsylvania. The series takes a timeline approach but keeps most of its focus on New York, as evidenced by its episode titles.

The premiere is “First Response,” starting with AA 11 hitting the North Tower, and the story continues into the tale of “The South Tower,” “Collapse,” “The Cloud,” “It’s All Gone, Kid” and “I’m Coming for You, Brother.”

Bogado admits that one of the biggest challenges of the series was in figuring out how much to feature how much of what happened at the Pentagon and on United 93 because those events were taking place at the same time as there were major developments with the World Trade Center — most notably its collapse — and they wanted to tell a “minute-by-minute story.” They relied mostly on interviews, such as with Alice Hoagland, whose son Mark Bingham called her from United 93, to tell that part of the day.

“It’s a tricky process,” Bogado says, “because you need to make some sacrifices sometimes in what you can include. These are 45 minute-long episodes, and you end up with just the most powerful and essential pieces. For such an important, huge story, you want all of it to be essential. And so that’s what was the guiding principle.”

The team also had the guidance of The 9/11 Memorial & Museum for their docuseries. Although Marsden says no one at the museum had “veto power” when it came to featured footage, she stresses the importance of their collaboration, both from an archival point of view and from a personal one.

Tom Canavan, a 9/11 survivor who worked in the building and then got a job in the museum is featured in the final episode of the docuseries talking about the importance of the space being sacred for those lost on the ground.

“When we first started, one of the things we did was, we went to the museum and we went through the exhibition,” Marsden says. “With archival materials, that was something that they helped us with immensely because they’ve been gathering archival material for years and years. And they would help us deal with more sensitive issues because those weren’t decisions that we took lightly, and these are things that they had been thinking about since they got going. We thought that it could creatively be a little bit of a North Star.”

“9/11: One Day in America” premieres August 29 at 9 p.m. on National Geographic.