On September 8th, 2001, I attended a rally in Union Square. The Parks 2001 campaign was urging all local candidates to take a strong stance on funding parks and open spaces citywide, and this event was the culmination of an aggressive, high-profile and fun effort.

The rally showcased what we love about New York's parks: They are democratic spaces. In addition to our political event, there were performers, tourists, birthday picnics, vendors and a dozen other "happenings" - small, medium and large. Our public spaces are sites for soapboxes and sermons, beatboxers and bargain-hunters, improvised eccentricity and casual community.

Four days later, on September 12th, I returned to Union Square again. At that time - with smoke heavy in the air, a burning scent that carried beyond midtown and a collectively-felt frightened confusion - the city was closed off (if our city can ever be "closed off") below 14th Street.

The park became a pool of humanity, where people from across the island drifted down - to help? to learn? to understand? -- and found they couldn't travel any further. There were impromptu candlelight vigils, walls of photographs, heaps of flowers, songs and tears and strangers embracing each other because they were fellow New Yorkers, just as sad, just as lost, just as in need of a hug.

And the park served its purpose as well as it had four days before: letting strangers become neighbors, letting us out of our homes and away from the repeated images on 24 hour news channels, and letting a city feel something together. That park - and our parks around the city - were the democratic spaces we needed.

The decade since has been a series of battles over preserving all our democratic spaces from threats of security theater, benevolent autocracy and the culture of fear. When White House Press Secretary Ari Fleischer warned that Americans better "watch what they say," he represented a front of jingoism that sought to chill free speech.

When Columbia faced protests for allowing Iranian President Mahmoud Ahmadinejad to speak, they confronted a threat to the role of our universities. When additional walls went up around City Hall, when more office buildings required IDs to enter, when NYPD began random searches of bags, we felt a real challenge to freedom of movement and assembly.

There have also been the moments that preserved our democratic spaces. When Mayor Giuliani was rebuffed in his suggestion to postpone elections, our system of democracy was preserved. When "free speech zones" sought to limit protests against the Iraq War and during the Republican Convention, protesters still gathered, risk arrest, and were heard.

When Bill Maher was removed from his network show, he found a new platform where he could really say what he wanted. When Dixie Chicks albums were burned at corporate-backed nationalistic mobs, the musicians made it into a movie.

The threats to our democratic spaces and vibrant, creative, passionate defenses of those spaces aren't unique to the past decade. That battle was born with our Republic and will continue beyond Sunday's memorial.

For many of us who were just out of college and embarking on "real life" ten years ago, these lessons of the fragility and resiliency of democracy have shaped our America and our New York -- and we learned them in the long shadows of towers that are fixed in our memories.

This Sunday, we remember the people who didn't know it would be their final day as they went to work; the heroism of those responders who raced in as any regular person would instinctively have run out; and the families that were changed forever by that morning.

We can debate the decisions made locally and nationally, the misadventures abroad, the memorializing at home. We can share stories of where we were when we heard, who we lost, who we found.

And we'll be sharing these stories in democratic spaces: at community events and in online forums, with neighbors we hardly know and the guy at the bodega who you know by face but not by name, at schools and through our free press and, of course, in our city's public spaces.

These are spaces we can never take for granted -- and which are essential if we are not just to live, but to live together.

Justin Krebs is a political organizer and writer based in New York City. He is the founder of Living Liberally, a nationwide network of 250 local clubs that create social events around progressive politics, and author of "538 Ways to Live, Work and Play Like a Liberal."