(File photo)

What is 15 years?

To those who have lived longer, a decade and a half can seem like a brief interlude. And yet it constitutes more than half of an entire generation: most high school freshmen had not been born by September 2001.

It’s worth pondering the significance of 15 years’ passing as we mark the anniversary of the September 11, 2001 terror attacks. Foremost is the remembrance of those who perished that day — nearly 3,000 victims in all, including 184 at the Pentagon. Those who were lost are forever mourned.

Many others who were directly impacted survived that day, but bear scars that will never completely heal. First responders who 15 years later can’t quite escape images of the day’s carnage and carry chronic ailments from the smoke and debris. Coworkers of the dead whose lives were spared by their tardiness for work. People who missed their flights that day. Workers at the Pentagon or World Trade Centers who got out in time. For those, the whys and what ifs linger.

More than any event of the last half-century, Americans remember exactly where we were when we heard about the attacks. Alexandrians who were outside on that spectacularly clear Tuesday morning reported feeling the impact of the crash. In the D.C. region, panic ensued, as we didn’t know if this was but the first wave of a broader series of attacks. Parents frantically tried to reach their children at school. Family members and friends tried to contact their loved ones at work.

But 15 years also provides us with the opportunity to evaluate meanings that go beyond the immediate experience of September 11. A sense of American invincibility died that day along with the victims. For the first time since Pearl Harbor, our country suffered a major attack by an external enemy on our own soil.

That day wound up launching us into two wars, in Afghanistan and Iraq, where we remain involved to this day. Like a mythical sea-monster, the tentacles that we chopped off in those endeavors were replaced by stronger and more plentiful threats. The terrorists of 2001 have been supplanted by today’s ISIS, an enemy even farther-reaching and more dangerous than Al-Qaeda.

Fifteen years later, we have sacrificed freedoms to the Patriot Act, NSA surveillance and airport searches in an effort to keep us safe. Our military and intelligence agencies have done a marvelous job of thwarting large-scale follow up attacks on American soil. And yet, as we look at major terrorist attacks around the world and smaller ones here at home, we feel — and likely are — less safe.

Birthdays, anniversaries and reunions all are emphasized in years that end in zero and five. Looking back in five-year intervals allows us to remember milestone events in a more meaningful way. When the commemorated events are happy ones, the subsequent gatherings are usually full of joy.

But it’s also important to gather and reflect on tragic events, as a group of firefighters who responded on September 11 — including Alexandria fire chief Robert Dubé — recently did when they gathered at the Pentagon. Alexandria will also hold a commemoration of 9/11 this Saturday at 5 p.m. at Market Square, located at 301 King St. Mayor Allison Silberberg and representatives from the city’s police and fire departments and the sheriff’s office will speak, and the Alexandria Harmonizers and City of Alexandria Pipes and Drums will perform.

And we must never forget that grace exists even in the most tragic of circumstances. From the ashes of September 11, 2001 rose the Alexandria Community Trust, established in part with funds donated by the family of Norma L. Steuerle, an Alexandria resident who died in the attack on the Pentagon. Each good work that ACT for Alexandria does is a tribute to Steuerle and those who died with her.

In remembering, we both honor and heal.