Marking the 19th anniversary of the 9/11 attacks that irreversibly changed U.S. history, we take a look at some of the harrowing statistics from the terrorist attacks.

On Sept 11, 2001, 19 men hijacked four fuel-loaded US commercial airplanes bound for west coast destinations. A total of 2,977 people were killed in New York City, Washington, DC, and outside of Shanksville, Pennsylvania.

The attack was orchestrated by al Qaeda leader Osama bin Laden.

The Twin Towers were built in 1970.

As of October 2019, 1,645 (60%) of 2,753 WTC victims' remains have been positively identified, according to the medical examiner's office.

The number of employees who died in Tower One: 1,402.

The number of employees who died in Tower Two: 614

The ratio of men to women who died: 3:1.

Age of the greatest number who died: between 35 and 39

Read more: Remembering the Irish Americans we lost in the 9/11 attacks

Number of people who lost a spouse or partner in the attacks: 1,609

Percentage of Americans who knew someone hurt or killed in the attacks: 20%

Number of people who died when American Airlines flight 11 from Boston, Massachusetts, to Los Angeles, California, crashed into the north tower of the World Trade Center: 92

Number of people who died when United Airlines flight 175  from Boston, Massachusetts, to Los Angeles, California, crashed into the south tower of the World Trade Center: 65

Number of people who died when United Airlines flight 93 from Newark, New Jersey, to San Francisco, California, crashed in rural southwest Pennsylvania: 45

Number of people who died when American Airlines flight 77,  from Washington to Los Angeles, crashed into the Pentagon: 64

Number of people killed in the Pentagon: 125

Source: New York Magazine and The Guardian newspaper

Read more: 9/11 attack on World Trade Center seared my soul

*Originally published in 2011.