9/11 is when the terrorist hijacked 4 passenger planes they crashed 2 of the planes into the Twin Towers, one in the Pentagon, and one in a field in Pennsylvania. The plane that crashed  in Pennsylvania had passengers who fought back and steered it in a field and saved many lives. The 2 planes that crashed in Manhattan made the Twin Towers fall. When one of the planes hit both of the towers a lot of people jumped and some got crushed from the flying debris. The plane that hit the Pentagon killed children and soldiers. It was one of the biggest attacks since the bombing of Pearl Harbor.