NEW YORK - It was a day that had been a long time coming, and for the community leaders who gathered Friday to dedicate a memorial at the once-forgotten grave site of thousands of African slaves, it was also a day of regret.

“Forgive us for disregarding your precious gifts to this world,” the Rev. James A. Forbes Jr., his voice amplified for the ceremony, said to the long-dead slaves and free blacks who were interred beneath lower Manhattan and then forgotten for decades as the city sprouted skyward above their remains.

It was a somber day for those gathered at the African Burial Ground memorial. Many speakers lamented the lack of recognition those buried there had experienced in life and after death, and they vowed to make the memorial a permanent reminder of their sacrifices.

Sixteen years after the remains were rediscovered, onlookers lined two city blocks on Friday for a chance to file through “The Door of Return,” the entryway named in contrast to the door of no return, the title once given to departure points where slaves were stolen away from their African homelands.

Walking through the narrow, reflective-granite structure, the memorial's first visitors stepped out into a sunken court engraved with a map of the lands and waters that once supported the slave trade, as well as the identifying details of some of the women, men and children buried nearby.

“Bid 'em in,” poet Maya Angelou sang to the crowd assembled for the dedication, telling the story of the auctioning of a young girl, stripped nude on the block.

“All of us are being 'bidded in' according to how we forget you,” she said to those interred beneath seven grassy mounds alongside the memorial. “And we will not forget you.”

Mayor Michael Bloomberg warned those assembled that forgetting might sometimes seem the easier route.The construction workers who stumbled across the site “brought to light one of the most uncomfortable and tragic truths in the history of our city,” Bloomberg said. “Part of atoning for such a terrible injustice is to acknowledge it.”

The Manhattan site was declared a national monument last year; New York City thrived during the slave trade and much of the early metropolis was built with slave labor.

At the dedication ceremony, Lt. Gov. David Paterson decried the lack of a national memorial in Washington, D.C., to mark the similar sacrifices slaves made throughout the nation.Organizers are still hoping to add a museum, which is in the planning phase.