It's been 20 years since the terror attack.
Today marks the 20th anniversary of the Septemer 11 attacks, otherwise known as 9/11.
This day 20 years ago, 2,977 people were killed when planes crashed into the World Trade Centre's twin towers.
The anniversary comes shortly after the end of the US-led war in Afghanistan.
That was launched around 20 years ago to root out Al-Qaeda, which are known to have carried out the 9/11 attacks.
US President Joe Biden gave a recorded speech to mark the day and commemorate the lives lost, and their families.
He said "Unity is the one thing that must never break. Unity is what makes us what we are."
20 years after September 11, 2001, we commemorate the 2,977 lives we lost and honor those who risked and gave their lives. As we saw in the days that followed, unity is our greatest strength. It’s what makes us who we are — and we can’t forget that. pic.twitter.com/WysK8m3LAb
— President Biden (@POTUS) September 10, 2021
Mr Biden is expected to visit each of the sites where hijacked planes crashed in 2001, to honor the victims of the attacks.
He and first lady Jill Biden will start in New York, to attend a ceremony at the site where the World Trade Center's twin towers once stood.
On September 11th 2001, nearly 3,000 people died when hijacked planes were flown into the World Trade Center and the Pentagon in a terrorist atrocity orchestrated by al Qaeda.@KayBurley takes a look at how events unfolded 20 years ago.
9/11 anniversary: https://t.co/dy6rtr2xIG pic.twitter.com/8zCNmuK4jJ
— Sky News (@SkyNews) September 11, 2021
He'll then will travel to Shanksville, Pennsylvania, where United Flight 93 crashed into a field after passengers overtook the hijackers and prevented another target from being hit.
Mr Biden will then return to Washington to visit the Pentagon, which was hit by another plane that day.
