Near the memorial plaza, police barricades blocked access to the site, even as life around the World Trade Center went on, workers rushing to their jobs and construction cranes looming over the area.
Name-reading, wreath-laying and other tributes were also held at the Pentagon and at the Flight 93 National Memorial in Shanksville.
"No matter how many years pass, this time comes around each year - and it's always the same," said Karen Hinson of Seaford, N.Y., who lost her 34-year-old brother, Michael Wittenstein, a Cantor Fitzgerald employee. "My brother was never found, so this is where he is for us," she said as she arrived for the ceremony with her family early Wednesday.
Memorial organizers expect to take primary responsibility for the ceremony next year. They said Wednesday they'll keep the focus onthe victims' loved ones, and aim to make the annual ceremony more low-key and perhaps private as the years go by.
The 12th anniversary also arrives with changes coming at the Flight 93 National Memorial in Shanksville, where officials gathered Tuesday to herald the start of construction on a visitor center. At the Pentagon, plans call for a morning ceremony for victims' relatives and survivors of the attacks and an afternoon observance for Pentagon workers.
Around the world, thousands of volunteers have pledged to do good deeds, honoring an anniversary that was designated a National Day of Service and Remembrance in 2009.