In Pictures: Americans Mark Anniversary of 9/11 Attacks

An American flag is seen in the engraved names of 9/11 victims that sits on the edge of the north reflecting pool at the 9/11 Memorial in lower Manhattan, New York, Sept. 11, 2019.

President Donald Trump and first lady Melania Trump participate in a moment of silence honoring the victims of the Sept. 11 terrorist attacks, on the South Lawn of the White House, Sept. 11, 2019, in Washington.

A boy holds up a photo of a 9/11 victim during the reading of victims' names during ceremonies at the 911 Memorial in lower Manhattan, New York, Sept. 11, 2019.

Officers carry an American flag into ceremonies commemorating at the 911 Memorial in lower Manhattan, New York, Sept. 11, 2019.

A man holds a photo of a victim during a ceremony marking the 18th anniversary of the attacks of Sept. 11, 2001 at the National September 11 Memorial, Sept. 11, 2019, in New York.

Members of Congress gather at the Capitol in Washington to observe the anniversary of the Sept. 11, 2001, terror attacks, Sept. 11, 2019.

A U.S. flag hanging from a steel girder, damaged in the Sept. 11, 2001 attacks on the World Trade Center, blows in the breeze at a memorial in Jersey City, New Jersey, Sept. 11, 2019

New York City Fire Department (FDNY) firefighters salute near the World Trade Center site on the 18th anniversary of the 9/11 attacks in lower Manhattan in New York, Sept. 11, 2019.

Airline employees visit the north reflecting pool during ceremonies at the 911 Memorial in lower Manhattan, New York, Sept. 11, 2019.

Crowd members participate in a moment of silence honoring the victims of the Sept. 11 terrorist attacks, at the Pentagon, Sept. 11, 2019..

Flowers rest on a bench bearing a name in memory of retired U.S. Army Lieutenant Colonel Gary Smith before a ceremony in observance of the 18th anniversary of the 9/11 attacks at the Pentagon in Washington, Sept. 11, 2019.

Visitors to the Flight 93 National Memorial in Shanksville, Pa., participate in a sunset memorial service, Sept. 10, 2019, as the nation prepares to mark the 18th anniversary of the 9/11 attacks.

People place flags into the egraved names of 911 victims at the edge of the south reflecting pool during ceremonies commemorating the 18th anniversary of the 9/11 at the 9/11 Memorial in lower Manhattan in New York, Sept. 11, 2019.

A man wipes away tears during ceremonies commemorating the 18th anniversary of the 9/11 attacks at the 911 Memorial in lower Manhattan in New York, Sept. 11, 2019.

Former marine Charlie Paul joins hundreds who lined Main Street in Freeport, Maine, for a 9/11 remembrance event, Sept. 11, 2019. Paul, who served as a radio operator during the Vietnam War, attends the Freeport flag ladies' final flag-waving ritual.