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It was a day of indelible images — apocalyptic, surreal, violent, ghostly, both monumental and profoundly personal. Wrenching to remember. Impossible to forget.

The terrorist attacks of 9/11 were captured in countless pictures by news photographers, bystanders, first responders, security cameras, FBI agents and others. Even an astronaut on the International Space Station took some.

Twenty years later, The Associated Press has its photographers’ frames from Sept. 11, 2001, when hijackers used commercial planes as missiles and crashed into New York’s World Trade Center, the Pentagon and a Pennsylvania field. The attacks killed nearly 3,000 people and toppled the trade center’s 110-story twin towers.

These photos document the enormity, chaos and emotion of 9/11 on every scale, from panoramic views of smoke rising over New York’s skyline to a close-up of the anxious, smudged face of a woman hastening down a street blanketed with ashen dust.

Street scenes chart escalating horror as people stare and weep at the burning skyscrapers, then run from the dust cloud billowing through lower Manhattan after one of them crumbles. Flames shoot from the windows of the Pentagon, a global symbol of military might that proved vulnerable to an attack by a handful of Islamic militants. A falling human form, almost silhouetted against one of the trade center towers, shows one of the most agonizing horrors of all.

Some show more intimate views of pain, but also humanity — an injured firefighter’s screaming face; a woman walking through the eerie blizzard of trade center debris with her arm around someone else’s shoulder; the then-deputy chief of the Army Reserve, Col. Malcolm Bruce Westcott, holding a comforting hand to Pentagon employee Racquel Kelley’s brow while assessing her for shock.

There are images of determination, including firefighters working amid the smoky rubble and a shopkeeper sweeping up the dust of catastrophe.

Finally, as night falls, people gaze across New York Harbor at the smoke, trying to make sense of what happened in front of their eyes. As we still are today.