NEW YORK—Once more, families gathered at ground zero, where nearly 3,000 people died on that bright September morning. Once more, there was an outpouring of grief. Once more, there was the sound of bells tolling in mourning and names being recited.

Eighteen years have passed since terrorists commandeered airplanes to take aim at the World Trade Center and bring them down.

The commemoration at ground zero — by now an annual rite of remembrance that follows a familiar, sombre script — began with bagpipers and drummers, marching in cadence. An honour guard carried the flag.

At 8:46 a.m., the time when the first plane slammed into the north tower, there was a moment of silence, the first of six marking the strikes at the trade centre and the Pentagon, and the plane crash in Shanksville, Pennsylvania, as well as the collapse of the twin towers in a blizzard of toxic dust and flaming debris.

Then, readers recited the names of the dead, one by one — brothers, sisters, cousins, mothers, husbands, wives. It is a ritual that takes about three and a half hours.

Rudy Giuliani, who was heralded for his leadership as mayor of New York when it was attacked, recalled the tragedy and the valour of that day.

“We will never forget 9/11,” he wrote on Twitter. “It was the worst attack on our nation since the War of 1812. It was the greatest display of domestic bravery in anyone’s memory. The enemy attacking us that day is still killing Americans. We honor all who have kept us safe.”

The 18th anniversary, not a major milestone like the fifth or the 10th, is taking place in an area that rebounded as it was rebuilt and, some say, as the country moved on. But for the families whose relatives were killed, the grief remains as piercing and profound as ever.

The anniversary came on another bright late-summer day in New York, but this time there were clouds hugging the horizon, in contrast to the clear blue sky of Sept. 11, 2001.

For many New Yorkers, the anniversary was just another day — which, of course, was what people thought the day of the attacks was going to be. In the morning, children went to school. Adults went to work. It was Primary Day in New York. Some stopped to vote on their way.

At the trade centre that morning, people picked up coffee and walked across the plaza, the way they always did. No one going through the revolving doors or stepping into the elevators knew then that it was the last time they would ever do that.

Nor did anyone there know that “Sept. 11” was about to become one of those dates that would summon personal memories as powerful as those associated with Nov. 22, 1963, the Friday on which President John F. Kennedy was assassinated, or perhaps Jan. 28, 1986, the Tuesday on which the space shuttle Challenger exploded little more than 1 minute after takeoff.

There are now 400 trees where the rubble was in 2001. For the ceremonies, loudspeakers have been hung — carefully — from many of the trees. The idea is that the names being read should be heard from anywhere on the memorial’s 8-acre site.

From the first 9/11 commemoration, long before a memorial and a museum paid tribute at the site, the reading has been a meaningful ritual that recognized each person caught in the tragedy of that day. But something is different this time: The 9/11 Memorial Glade, dedicated in May.

It honours another segment of the 9/11 community, those who were exposed to toxins in the aftermath of the attacks — people who worked in the twin towers and escaped; police officers and firefighters who went through rubble that burned for more than three months; and residents of lower Manhattan who breathed the same air. Some have developed chronic illnesses. Some have died.

The Glade, a series of large stone “monoliths” inlaid with steel from the original trade centre, was dedicated on another grim anniversary, the 17th anniversary of the official end of the recovery mission at ground zero. At 13 to 18 tons apiece, the monoliths were so heavy that they had to be installed with two cranes that lifted them over the tall white oak trees on the plaza.

The platform for the readers will stand in the shadow of a One World Trade Center that is no longer new — people took note of its rise toward the sky at earlier ceremonies, but the construction fences that once lined the area are long gone. The new One World Trade Center opened five years ago, the observatory on its top floors more recently.

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There will be other observances Wednesday morning. At Trinity Church at the head of Wall Street, the rector, the Rev. Dr. William Lupfer, will ring the Bell of Hope, given to the city by Michael Oliver, who was the Lord Mayor of London in 2002, a year after the attacks.

At ground zero, “The Star-Spangled Banner” is to be sung by Kassidy Rieder, a senior at the Long Island School for the Arts who is in her third year in the pre-college program at the Juilliard School.

She is too young to remember Sept. 11. Her mother, Nancy Collins, is a police officer who worked at ground zero during the search and recovery operation — until she discovered that she was expecting Kassidy.