These iconic images from 9/11 are truly unforgettable

The country watched in horror as hijacked airplanes crashed into the World Trade Center in New York City, the Pentagon and a field in Shanksville, Pa.

Many Americans remember exactly where they were during the terrorist attacks on Sept. 11, 2001. 

The country watched in horror as hijacked airplanes crashed into the World Trade Center in New York City, the Pentagon in Washington, D.C., and a field in Shanksville, Pennsylvania.  The attack killed 2,996 people, making it the deadliest foreign attack ever on U.S. soil.

Another 10,000 first responders and others who were in the World Trade Center area have been diagnosed with cancer. And more than 2,000 deaths have been attributed to 9/11 illnesses. 

The attacks prompted a new focus by the government on fighting terrorism and a host of new security measures in different parts of everyday American life. 

Each anniversary brings a resurgence of memories from that fateful day, but the heartbreaking visuals are particularly striking. Here are the most memorable photos from the September 11 attacks.

President George W. Bush's Chief of Staff Andy Card whispers into the ear of the president, giving him word of the plane crashes into the World Trade Center, during a visit to the Emma E. Booker Elementary School in Sarasota, Fla.
President George W. Bush's Chief of Staff Andy Card whispers into the ear of the president, giving him word of the plane crashes into the... President George W. Bush's Chief of Staff Andy Card whispers into the ear of the president, giving him word of the plane crashes into the World Trade Center, during a visit to the Emma E. Booker Elementary School in Sarasota, Fla.
Doug Mills, AP
Two women hold each other as they watch the World Trade Center burn.
Two women hold each other as they watch the World Trade Center burn.
Ernesto Mora, AP
Smoke pours from the twin towers of the World Trade Center.
Smoke pours from the twin towers of the World Trade Center.
Robert Giroux, Getty Images
People run from the collapse of one of the twin towers.
People run from the collapse of one of the twin towers.
Suzanne Plunkett, AP
A person falls from the north tower of New York's World Trade Center.
A person falls from the north tower of New York's World Trade Center.
Richard Drew, AP
Marcy Borders is covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York.
Marcy Borders is covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York.
Stan Honda, AFP/Getty Images
A man coughs as he is coated with ash and debris from the collapse of the World Trade Center.
A man coughs as he is coated with ash and debris from the collapse of the World Trade Center.
Amy Sancetta, AP
A helicopter flies over the Pentagon in Washington on Sept. 11, 2001 as smoke billows over the building.
A helicopter flies over the Pentagon in Washington on Sept. 11, 2001 as smoke billows over the building.
Heesoon Yim, AP
A man calls out for survivors amid the rubble of the first World Trade Center tower in New York.
A man calls out for survivors amid the rubble of the first World Trade Center tower in New York.
Doug Kanter, AFP/Getty Images
Firefighters raise a flag at the World Trade Center in New York.
Firefighters raise a flag at the World Trade Center in New York.
Thomas E. Franklin, The Bergen Record