Events at all three sites included a reading of the names of those who died.
Other communities around the country were holding candlelight vigils, interfaith services and other commemorations. Some Americans are joining in volunteer projects on a day that is federally recognized as Patriot Day and a National Day of Service and Remembrance.
"America itself changed that day," Biden told a somber crowd in the rain outside the Pentagon. "But what we will not change, and never will, is the character of this nation that the terrorist thought they could wound."
