At his second stop to commemorate the 10th anniversary of 9/11, President Obama honored the passengers who died aboard United Flight 93 in Shanksville, Pa.

The president took part in a wreath-laying ceremony and greeted some of the families in attendance at the memorial site honoring the victims.

Obama, along with his wife, Michelle, visited a wall listing the names of every person who was killed in the crash. The plane, which U.S. officials believe terrorists wanted to use to strike either the White House or the Capitol building, crashed in Shanksville after passengers and crew stormed the cockpit. The incident is considered an iconic moment, a symbol of the heroism displayed by many Americans on 9/11.

During the stop, the president did not speak. He will address a concert at the Kennedy Center in Washington tonight. A White House senior adviser said the president’s speech will reflect on how the country has changed since 9/11.

As the day of remembrance continues, U.S. officials remain on high alert working to keep the public safe. Earlier in the day at the White House, Obama’s counter-terror adviser, John Brennan, held a meeting to review counter-terrorism preparations and the nature of the threats against the United States.

“This is a 24/7, round-the-clock effort by all elements of the U.S. counterterrorism community,” Brennan said on the CBS program “Face the Nation. “We’re looking at a number of leads. We are looking at travel data, other types of pieces of information and trying to correlate them against other reporting that is coming in. And so we’re pursuing a number of leads. Again, it’s not confirmed but we’re not relaxing at all.”