The United State of America President Joe Biden commemorated the 20th anniversary of the September 11 attacks on the United States on Saturday with visits to each of the sites where hijacked planes crashed in 2001, honoring the victims of the devastating assault.

Biden began the day in New York, where he and first lady Jill Biden attended a ceremony at the site where the World Trade Center’s twin towers once stood before planes struck the buildings and caused them to collapse. They then flew to Shanksville, Pennsylvania, and were scheduled to return to the Washington area and visit the Pentagon.

At the World Trade Center site, the New York Police Department pipes and drums band played “Hard Times Come Again No More” a U.S. folk song from the 1850s. Bruce Springsteen, playing an acoustic guitar, sang “I’ll See You in My Dreams”.

The Bidens, withformer Presidents Bill Clinton and Barack Obama and former first ladies Hillary Clinton and Michelle Obama,shared a moment of silence with the crowd at 8:46 to mark the time that the first plane hit.

Nearly 3,000 people died in the attacks in New York, at the Pentagon and in Pennsylvania, where passengers on United Flight 93 overcame the hijackers and the plane crashed in a field, preventing another target from being hit.

In New York City, on a clear, beautiful day similar to the weather 20 years ago, relatives read a list of the people who died at the towers.

Biden, head bowed, did not make remarks. Rudy Giuliani, the mayor of New York at the time of the attacks, attended the ceremony. Former President Donald Trump, a New York native, did not.

In Shanksville, the Bidens participated in a wreath-laying ceremony at the Flight 93 National Memorial where names of the deceased are etched on a marble wall.

Also in Shanksville, in rare public comments, former President George W. Bush, who led the country at the time of the attacks, warned of the threat of domestic terrorism. Recalling the unity of the American people in the days after 9/11, he called for a return to that spirit amid growing political division in the country.

Vice President Kamala Harris said the passengers and crew members who died in Shanksville focused on common humanity during a time of terror. “It is my hope and prayer that we continue to honor their courage, their conviction, with our own; that we honor their unity by strengthening our common bonds, by strengthening our global partnerships.”

Later in the day Biden was to visit the Pentagon, the symbol of U.S. military might that was pierced by another of the planes that were used as missiles that day.

The anniversary comes shortly after the end of the U.S.-led war in Afghanistan that Bush launched some 20 years ago to root out al Qaeda, which carried out the 9/11 attacks.

Biden’s withdrawal of U.S. troops in August, months after a deadline set by his Republican predecessor Trump, and the resulting rapid fall of the country to the Taliban has drawn criticism from members of both political parties.