President Donald Trump and first lady Melania Trump attended a somber ceremony at the Pentagon on Thursday, where 184 service members and civilians killed when hijackers steered a jetliner into the headquarters of the U.S. military were honored.

“Today, as one nation, we renew our sacred vow that we will never forget Sept. 11, 2001,” Trump said during the observance, which took place in an internal courtyard of the building rather than its traditional location outside its walls near the building’s 9/11 memorial.

The president, in his remarks, recounted moments from that day, including snippets of conversations from passengers who were aboard the hijacked airplanes.

“The enemy will always fail,” he added.