Sunday marks 15 years since 9/11, the devastating terrorist attacks on the United States that changed the nation forever. On Sept. 11, 2001, hijackers took control of four airplanes and crashed them into the World Trade Center, Pentagon and a field near Shanksville, Pennsylvania, killing almost 3,000 people and kickstarting a new age of security.

"Our fellow citizens, our way of life, our very freedom came under attack in a series of deliberate and deadly terrorist acts," then-President George W. Bush said in an address the night of the disaster. "The pictures of airplanes flying into buildings, fires burning, huge structures collapsing, have filled us with disbelief, terrible sadness, and a quiet, unyielding anger. These acts of mass murder were intended to frighten our nation into chaos and retreat. But they have failed; our country is strong."

As the Twin Towers collapsed and rescuers rushed to what became Ground Zero, photographers were on hand to capture the scene. The pictures, displayed on TV for weeks in 2001 and immortalized in newspapers, remind people today of the devastation.

"I think many of the images from 9/11 still convey the rawness and brutality of the attack," Clifford Chanin, an executive at New York City's National September 11 Memorial and Museum, told National Geographic in 2011. "It seems to me that they still have the capacity to shock."

Whether taken by amateur passers-by or professional photographers, pictures from 9/11 abound on the internet, circulating yearly on the anniversary of the attacks.

On Sunday, Americans will remember the tragedy in different ways — Vice President Joe Biden will honor emergency officials, English firefighters will go silent and the 9/11 memorial will show a searchlight tribute, according to Time — and you can join in by looking at iconic images. Above, click through some of the most striking photos of 9/11, collected from Getty Images and Reuters.