A solemn ceremony marking the end of an eight-month cleanup of what had been the World Trade Center began with a bell sounding out the 5-5-5-5 fire code — four sets of five rings, in memory of 343 fallen firefighters lost at ground zero.

The first bell rang at precisely 10:29 a.m., the time that the second tower collapsed in a screech of twisting steel and falling concrete on Sept. 11.

An empty, flag-draped stretcher symbolizing the missing was then carried up a 500-foot ramp from the pit where workers labored around the clock. The stretcher was loaded into an FDNY ambulance as a dozen pall bearers saluted. A truck carrying the last beam from the site followed the ambulance up the ramp.

The sounds of taps, played by police and fire buglers, floated across the warm May morning before bagpipers played "America the Beautiful."

Thousands gathered at the site, now a seven-story pit and once the basement of the twin skyscrapers that anchored lower Manhattan. Mayor Michael Bloomberg and his predecessor, Rudolph Giuliani, were among the many public officials at the event.

"It was tough to come here every day and now it's tough to leave," firefighter John Keating said.

Of the more than 2,800 people killed in the terrorist attack, remains of 1,102 have been identified. Nearly 20,000 body parts have been recovered.

City officials said the sifting for body parts in a landfill and the identification process will go on for months. Those human remains that cannot be identified will be retained, in case new technology someday makes it possible.

At the ceremony, a flatbed truck carrying the trade center's last steel beam followed the ambulance. The beam stood until Tuesday night, when it was cut down during a ceremony for ground zero workers.

The 30-foot column survived when the towers collapsed into a mountain of 1.8 million tons of rubble. For months it was buried in debris, but it was revealed as the rubble disappeared, still standing where it was planted when the south tower was built. The beam, set on the truck and draped with a black cloth, American flag and bouquet of flowers, was being taken to a Kennedy Airport hangar for storage.

To accommodate those who could not attend the ceremony, the family groups have planned their own service at ground zero on Sunday.

What to do with the site after the ceremony is under discussion. Control of the site will revert from the city to the Port Authority of New York and New Jersey, which owns the land.

Last week, the Port Authority and the Lower Manhattan Development Corp. announced the choice of architectural firm Beyer Blinder Belle as the urban planning consultant that will assist their staffs in producing a plan. Beyer Blinder Belle will submit up to six proposals by July 1; a final plan is supposed to be chosen by Dec. 1.