From left, Bill and Hillary Clinton, Barack and Michelle Obama, President Joe Biden and first lady Jill Biden, former New York Mayor Michael Bloomberg and his partner Diana Taylor, and House Speaker Nancy Pelosi participate in a moment of silence at the National September 11 Memorial and Museum in New York on Saturday, September 11.
Chip Somodevilla/Getty Images

In pictures: Remembering 9/11, 20 years on

Updated 12:07 AM ET, Sun September 12, 2021

From left, Bill and Hillary Clinton, Barack and Michelle Obama, President Joe Biden and first lady Jill Biden, former New York Mayor Michael Bloomberg and his partner Diana Taylor, and House Speaker Nancy Pelosi participate in a moment of silence at the National September 11 Memorial and Museum in New York on Saturday, September 11.
Chip Somodevilla/Getty Images

It has been 20 years since the September 11 attacks.

Across the country, people are pausing to honor the victims and reflect on the day.

Nearly 3,000 people were killed when hijackers crashed planes into the World Trade Center, the Pentagon and a field in Pennsylvania.

"These memorials are really important," said President Joe Biden, who visited all three sites. "But they're also incredibly difficult for the people affected by them, because it brings back the moment they got the phone call. It brings back the instant they got the news, no matter how years go by."