NEW YORK - It's been 16 years since the September 11th terror attacks.
Ceremonies took place across the city and around the country to remember those who died at the World Trade Center, the Pentagon and in Shanksville, Pennsylvania.
Thousands gathered for the annual reading of the names at the National September 11th Museum and Memorial.
It began with a moment of silence at 8:46 a.m., the time American Airlines Flight 11 hit the North Tower.
Houses of worship across the city also rang their bells at that time.
Moments of silence followed for when the second plane struck the South Tower, for when each tower fell, and for when the attacks at the Pentagon and in Pennsylvania.
President Donald Trump, who attended the memorial service at the Pentagon, says the country lost heroes during the attack.
"Each of those brave Americans died as they had lived as heroes, doing their duty and protecting us and our country. We mourn them, we honor them and we pledge to never, ever forget them," Trump said.
Hundreds also gathered for an observance in Shanksville.
That's where united Flight 93 crashed as passengers and crew attempted to take the plane back from the hijackers.
Vice President Mike Pence referred to them as heroes.
"Men and women who looked evil squarely in the eye, and without regard to their personal safety, they rushed forward to save lives. They were mothers and fathers, your brothers and sisters, sons daughters of every walk of life, from every background," Pence said.
United Flight 93 was the only hijacked plane not to crash into its intended target on September 11, 2001.
All 40 passengers and crew onboard were killed in the crash.
The annual Tribute in Light will illuminate the night sky Monday night.
The lights go on at sunset and will fade away at dawn early Tuesday.
They can be seen for miles from their location at West and Morris Streets in Lower Manhattan.
The art installation first went up in March of 2002.
Governor Andrew Cuomo has also ordered that flags be flown at half-staff in honor of the attack victims.