Flags flew, prayers were issued and a few tears were shed Monday evening on Beinecke Plaza, as about 150 people gathered to commemorate the five-year anniversary of the Sept. 11, 2001, terrorist attacks. Eighteen hundred twenty-eight days after the tragedy, the evening seemed designed for a memorial: Blue sky floated over white marble, a quiet breeze carried solemn speeches, and a stark war marker stood behind uniformed Yale police, a head-scarfed chaplain and a music student swaying over her violin.

But even as the strains of music echoed on the Beinecke marble, boys in gym shorts and girls in spandex wandered out of Commons, unaware. They paused and whispered, not sure what to make of the solemn crowd, and looked around for the least awkward exit.

No one who was alive for it will ever forget Sept. 11, 2001. But five years later, it is not clear how actively many people remember the event that may come to define their generation.

All the politicians who could have keynoted already had speaking engagements for the day. Students across campus cracked open their Blue Books for the home stretch of shopping period. President Richard Levin was on a fundraising tour.

As candlelit vigils have given way to brief moments of silence, students, faculty and staff at Yale are left to answer the same questions: How should we continue to memorialize Sept. 11, and when will it be OK to stop?

Yesterday’s memorial, which was co-sponsored by the Yale College Democrats and Yale College Republicans, originated as part of the Foundation for Defense of Democracy’s undergraduate fellowship. Created to examine how democracies protect themselves against terrorism, the nonpartisan nonprofit sends 40-50 students to Israel every summer. The program aims to help students “enlighten the debate about the need to defend ourselves” by studying the society that has been “fighting Islamist terror longer than anyone else,” said David Silverstein, the foundation’s vice president of campus education.

“The reason for staging a 9/11 memorial is to ensure that students and the larger group of folks on campus understand the nature of the threat and will not become complacent in the face of that threat,” Silverstein said.

John DiMaio ’09 and Edward Walsh ’07, two of the foundation’s 2006 fellows, planned the memorial as part of the foundation’s yearlong program, which, in addition to the summer in Israel, includes organizing campus events to promote awareness of responses to terrorism. Envisioned by DiMaio as “a time for everyone to come together and remember what happened,” the evening took on a more personal significance for the two fellows.

“I was surprised that no one was really organizing a Yale University memorial for the event, and it became an obligation outside of the fellowship — as a Yale student and as an American — to keep that day in our memories,” DiMaio said.

At 6:30 p.m., the crowd stood for the beginning of the ceremony, as the Yale police undertook a hushed posting of colors, raising flags in a tribute to their fallen colleagues.

“We lost a lot of brothers and sisters on that day, and we want to do anything we can do to perpetuate their memory,” Yale Police Department Lt. Michael Patten said.

A rendition of the national anthem, sung at a deliberate pace by Elizabeth Brandwood ’07, and a minute-by-minute account of the events of the morning of Sept. 11, issued by Walsh, followed the posting. After a moment of silence and a haunting violin performance by Alex Weill ’09, University Chaplain Frederick Streets took the podium to praise Yale students’ efforts to grapple with the aftermath of the attacks.

“Those of us who are not college students … are inspired by what we see you do,” Streets said. “Each of us have our own way of trying to respond to what these events mean for the world.”

Associate University Chaplain Shamsad Sheikh followed Streets with a reading from an Islamic text.

“Remember that whatever you learn is from the mercy of God,” she read. “Each is bound up with all.”

That human link was expanded upon by the text of a speech written by Levin, which DiMaio read aloud.

“Yale is a strong community, and tonight we are also part of a broader community that spans the globe, a community of shared memory and hope,” DiMaio read. “As we commemorate what was lost, let us rededicate ourselves to the preservation of freedom and hope for all humankind.”

Rounding out the speakers’ lineup, Rabbi James Ponet, the director of Yale Hillel and the University’s Jewish chaplain, expressed his happiness that people from different religious backgrounds could unite to commemorate Sept. 11.

“I’m conscious that three Abrahamic faiths seem to be at the heart of the problem and at the heart of what we hope to be the solution for hatred,” Ponet said. “Let us know that we came together today here on Beinecke Plaza on the fifth anniversary of an event all too religious, all too horrible, as religionists seeking to find a common way towards peace.”

As taps sounded from somewhere on Cross Campus, the flags were carried out of sight. Two Yale police officers in ceremonial blue knelt beside a crying girl. Students in suits folded up plastic chairs. The crowd dispersed, heads bowed and arms folded tightly, each reflecting on the tribute they had witnessed.

Brendan Gants ’08, president of the Yale College Democrats, said he was pleased by the event’s tenor.

“We were assured that it would not be a political event, but a somber tribute and memorial to those who lost their lives on Sept. 11, and that’s exactly what it was,” he said. “I think that this event should serve as a reminder that whatever anyone’s political leanings or backgrounds or biases may be, all Americans understand the evil that confronts us in terrorism and the seriousness of our response to that.”

Spencer Sherman ’08, who attended the event, said it was important to him to have the opportunity to look beyond discussion sections and homework, especially since the intervening years have begun to transform what was once “a direct emotional wound” into a “distant memory.”

During those years, DiMaio said, the inevitable politicizing of that traumatic day have muddied many students’ recollections.

“It feels like what has happened between Sept. 11 and now has taken the focus off the events of 9/11 and put it elsewhere,” DiMaio said. “Sept. 11 should be remembered for what it was and not for what came after.”

Situated on the outer edge of New York City’s commuter radius, New Haven felt the post-9/11 vulnerability more than many cities, said Alan Plattus, a professor at the Yale School of Architecture. But five years later, outside of a small circle of public officials, daily life in New Haven has long since returned to normal.

“I think the average American city stopped and looked at itself in a different way for a while — maybe a long while — but in the end, we’ve gotten back to our lives and our businesses, and on the typical day in a typical city, I don’t think there is an appreciable difference in urban life,” Plattus said. “Cities are constantly reminded that they are subject to catastrophes of various kinds. … That is never going to change, whether it’s 1666 in London or 2001 in New York City.”

But appreciable difference or not, many said the day has made a permanent impact on how they view the world.

“This is a watershed mark in our generation,” said Alex Yergin ’07, president of Yale College Republicans. “We are united because years down the line, we will remember where we were when we heard about Sept. 11.”

Alex Schwartz ’09, a New York City native, chose not to attend last night’s memorial. Instead, Schwartz said, she read all of The New York Times’ profiles of Sept. 11 victims as a way of remembering the day. In the future, Schwartz said, memorialization of Sept. 11 will become more a matter of personal reflection and less a public political display.

Sitting in class yesterday morning, Schwartz said, she overheard one of her classmates as the girl began to take notes. “Oh,” she said, “it’s Sept. 11.” In that moment, Schwartz said, she knew the student was reliving their own personal Sept. 11.

And so the public commemoration also becomes a private one.

As he delivered the minute-by-minute recap of the events of Sept. 11, Walsh remembered third-period philosophy in high school, when he heard about the attacks and started asking himself the questions that would eventually turn the self-described “math and science person” into a political junkie.

As he led the Yale police in posting the colors, Patten remembered news of the first plane crash coming in over the static of his radio.

As he recited the text of Levin’s prepared speech, DiMaio remembered leaving classroom H4 in his high school’s basement, at first convinced that the plane crash was a reprise of a World War II accident in which a small warplane got lost and crashed into the Empire State Building.

“I think the actual memory of the isolated event in itself is always going to be a private one,” Schwartz said.