Two planes hit the Twin Towers of the World Trade Center, with the first striking the North Tower at 8:46 am, and the second hitting the South Tower shortly afterwards at 9:03 am.
In under two hours, both 110-story towers had collapsed.
A third plane struck the western face of the Pentagon, the headquarters of the US military in Washington DC, at 9:37 am.
The fourth plane crash landed in a field in Pennsylvania after passengers attempted to regain control. It’s believed that the fourth plane was meant to target either the White House or the Capitol Building. All 40 passengers and crew, as well as the four hijackers died.
How many people died?
A total of 2,996 people were killed in the 9/11 attacks, including the 19 hijackers that took control of the airplanes. The majority of the fatalities occurred in New York, and more than 6,000 additional people were injured.
All passengers and crew of the four planes involved in the attack were killed, and a further 2,606 died at the Twin Towers, either at the scene or later on from their injuries. At the Pentagon, 125 people also lost their lives, most of whom worked for the United States Army or the United States Navy.
The FBI states that more than 400 first responders, including 60 law enforcement officers, were killed.
The youngest victim of the attack was Christine Lee Hanson, who was only two years old. She died on Flight 175, which crashed into the south tower of the World Trade Center, along with her parents Peter and Sue.
The eldest was 82-year-old Robert Norton, who was on Flight 77, which crashed into the Pentagon, with his wife Jacqueline. They were travelling to a wedding.
Countries from around the world lost citizens in the attack, including the UK with 67 deaths, Greece with 39 deaths, Australia with 11 deaths and South Korea with 28 deaths.
To this day, 9/11 remains as the deadliest terror attack in history.
What is the 9/11 Memorial Museum?
The 9/11 Memorial and Museum opened on 11 September 2011, on the 10th anniversary of the attacks.
The memorial is situated where the Twin Towers once stood, and was designed by two architects, Michael Arad and Peter Walker.
The Memorial Plaza surrounds two large reflecting pools set where the North and South Towers used to be. The pools each feature a 30 foot waterfall, making them the largest man-made waterfalls in North America.
The names of those who were killed in the 9/11 attacks in New York, the Pentagon, on Flight 93 and those killed in the bombing at the World Trade Centre, are carved into the bronze around the edges of the pool.
On the 9/11 Memorial and Museum website, the names of every person are listed as they appear inscribed in bronze on the memorial.
The site explains: “Every name can be located by the panel on which it is inscribed. A panel address is comprised of the letter N or S (N for north pool, S for south pool) followed by a number one through 76.”
In 2014, the 9/11 Memorial Museum opened, where visitors can see artifacts from the World Trade Centre and 9/11 attack, interactive exhibitions and programmes that feature individual and collective stories relating to the experiences of survivors, eyewitnesses and first responders.
“The 9/11 Memorial Museum tells the story of 9/11 through media, narratives, and a collection of monumental and authentic artifacts, presenting visitors with personal stories of loss, recovery, and hope,” the site says.
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