Sunday marks the 15-year anniversary of the Sept. 11 attacks, the deadliest attack on American soil since the Peal Harbor bombings in 1941, and the deadliest terror attacks in world history.
President Obama memorialized the victims in a speech outside the Pentagon on Sunday, remembering the "3,000 beautiful lives" that were lost.
"We wonder how their lives might have unfolded, how their dreams might have taken shape," he said. "We know that our diversity, our patchwork heritage, is not a weakness [...] this is the America that was attacked that September morning. This is the America that we must remain true to."
Democratic presidential nominee Hillary Clinton, who served as a New York senator during the attacks, told CNN the image of the buildings collapsing was "as close to a depiction of hell" she'd "ever personally seen."
"We saw this curtain of smoke that was stretched across the island," she said. "It would occasionally be broken by a firefighter coming out. I remember this one image so indelibly, you know, dragging his axe."
Below, other words of remembrance from top officials and thinkers.