Standing where the World Trade Center towers used to be, New York Mayor Michael Bloomberg declared a minute of silence for the nearly 3,000 people killed there, as well as in Washington and Pennsylvania.
Bloomberg said the service would be led by victims' "spouses, partners and significant others to lead these ceremonies -- not in the first flush of despair, but with the saving grace of memory."
Several of the people quoted poetry or song lyrics in their tributes, which were interspersed with readings by New York Gov. George Pataki and New Jersey Gov. Jon Corzine.
Rudolph Giuliani, who was New York's mayor when the attacks came, also spoke of the victims and the emergency crews who died trying to help them.
"We also have come to be ever mindful of the courage of those who grieve for them and the light that still lives in their hearts," Giuliani said.