They streamed across a metal and concrete walkway to the place their loved ones perished, carrying flowers, laminated pictures of the dead and a burden of grief few can imagine, Denis Staunton writes from New York.
They were led by pipers from the New York Police Department in green kilts and berets with green and orange hackles, playing Irish airs, including Thomas Moore's Let Erin Remember.
It was a clear, bright morning with an unseasonable chill in the air, just like the day five years ago that shattered these mourners' lives and changed the world.
As the names of each of those who died at the World Trade Center on 9/11 were spoken by survivors, groups of relatives approached two reflective pools marking the footprints of the towers that collapsed. As they tossed roses on to the pools and stopped to reflect, many broke down, comforting one another with hugs as children, many too young to remember the parents they lost, looked on in silence.
A massive police officer strode towards one of the pools, a picture of strength until he knelt and began to sob uncontrollably.
One man held aloft a photograph with the words "My wife Edna Cintron. I miss you."
The city's mayor, Michael Bloomberg, was there with his predecessor Rudy Giuliani, along with New York senators Hillary Clinton and Chuck Schumer. The politicians knew, however, that yesterday's ceremony was not about them, or President George Bush, or even the "war on terror", but about remembering those who died as spouses, partners and friends, as sons and daughters, and as mothers and fathers.
The recital of names stopped four times as bells tolled to mark the moments when the two planes crashed and when each of the towers collapsed. As the last names were read out, someone released a few red, helium-filled balloons that soared upwards towards the sky.
Outside Ground Zero, life in New York went on as normal, testimony to the remarkable recovery the city has made since the attacks. Commemorations continued throughout the day, including a city-wide singalong of the Beatles' All You Need Is Love.