New Orleans residents Sunday marked five years since Hurricane Katrina and the devastating floods that followed with a memorial service in the Lower Ninth Ward, where the storm hit hardest.

"We lost 1,800 people in the worst manmade disaster ever to hit this country," said New Orleans Mayor, Mitch Landrieu, sheltered from light rain by an umbrella as he addressed a crowd of hundreds.

"We're still standing, and we're never, ever, ever going to give up. If we can't rebuild the lower nine, then we can't rebuild America."

The crowd marched up the Judge Seeber Bridge to drop a wreath into the Industrial Canal, which breached the levees and came crashing into the neighborhood in 2005, carrying off whole blocks of houses in fierce torrents.

The bridge served as a high ground gathering point for Lower Ninth Ward residents during the hurricane.

Landrieu, who stood on the bridge in the aftermath of the storm and the devastating flooding that followed, recalled the horror and trauma of the disaster.

"I can remember vividly the cries that were coming through the neighborhood," he said. "And people coming like apparitions out of the water, heads first, then shoulders, and arms, carrying black garbage bags."

The marchers stepped across the Seeber Bridge accompanied by the Carver Rams brass band, which played Kool & The Gang's "Celebration" and Michael Jackson's "Don't Stop Til You Get Enough."

Those marching behind the band formed a "second line," a New Orleans tradition sometimes described as a jazz funeral without a body.

Members of the brass band lead the procession, followed by the "second line" of people there to enjoy the music -- dancing, twirling parasols or waving handkerchiefs in the air.

Lower Ninth Ward resident Robert Greene Sr. danced in the second line, ringing bells he had collected from the past Katrina anniversaries.

His mother died on the roof of his house on Tennessee Street, and his granddaughter drowned in the floodwaters, waiting for help back in 2005.

But despite the pain of his memories, he was pleased to hear the band playing "Celebration."

"That's what we do in New Orleans," he said. "We celebrate because we can't hold on to the tragedy."

Greene now lives in a house built by Brad Pitt's Make It Right foundation, which has worked to build low-cost, sustainable housing for those who lost homes in the storm.

Senator Mary Landrieu, Mitch Landrieu's sister, described Pitt as "the angel of the ninth ward" and Greene was pleased, walking back into the neighborhood, that his house was no longer visible, obscured by some 50 other Make It Right homes.

"People are coming back," he said. "And there are more people here at the memorial this year than there ever have been before. Because we got organized and came together."

The day concluded with a memorial service combining commemoration with celebration at the Mahalia Jackson Theater in Armstrong Park, in the heart of downtown New Orleans.

"We must face the truth that in the fifth year of the 21st century, for four horrific days, there was anarchy on the streets of America," said Mayor Landrieu. "The levees broke and our government failed. It's a moment we should never forget and one that we should never repeat."

"America, hear this," Landrieu continued. "The people of New Orleans are still standing, unbowed and unbroken."

Landrieu said the storm also taught New Orleans residents valuable lessons about the value of being good neighbors and cooperation between people of different backgrounds.

They learned that the true value of their lives was defined by relationships, and not material possessions, he said.

"We all need to spend more time together, than apart," said Landrieu. "And we must learn to listen and value what we all have to say. And when we truly listen, do you know what we will hear? We will hear and we will learn the beautiful lesson that Katrina taught us all. We are all the same."