Wednesday morning marked the 12th anniversary of September 11.

Each year, the memories of those harrowing hours and days slip a bit further into the recesses of history. They will always be represented on video and through the digital records of websites and e-mails, of course, but there’s no way to fully preserve the emotions of the day itself that live inside each human being who witnessed and were old enough to process the events:

The way we felt as those first images of a real-life towering inferno assaulted our sense; the shock and alarm as another plane plunged across the screen and into the next building; the awful awareness that the lives of so many innocent souls had been deliberately extinguished in an unprecedented public execution.

We remember the sounds from that day, too. The first-hour pronouncements by co-workers that “this means war.” The gasps as both towers fell. The sound of silence from above as the rumble of air traffic came to an abrupt and extended stop.

For those too young to remember, or not yet born, the day itself will no doubt hold a different meaning. It is for us who were conscious then to pass along that part of the story that only we can know: The resolve and solidarity that quickly replaced the fear and foreboding. The leadership and courage that defied party label. The fleeting, but still authentic, sense of unity and patriotism.

Last April’s horrible events on Boylston Street delivered an all-too-intimate reminder of how we felt that day. But Sept. 11, 2001, stands as a singular event in our nation’s history and imagination. We must never forget, not should we allow it to be cheapened, commercialized, or trivialized. It must remain a day of solemn reflection on what we as a nation experienced, how we have changed, and how we must continue protect future generations from harm.