The twin towers, which opened on April 4, 1973 in Lower Manhattan, New York City, were the tallest buildings in the world at 1,368 feet and 1,362 feet.

After the airplanes hit, both 110-storied towers fell within an hour and forty two minutes. The debris and fire from the collapse destroyed or partially damaged all the other buildings in the World Trade Center complex including the 7 World Trade Center.

One World Trade Center, which was completed on May 20, 2013, proudly stands today at the 9/11 Ground Zero as the symbol of resilience of the American people.

Here are some of the haunting photos from the day that we can never forget.

Trump's new Afghanistan strategy: "Killing terrorists"