It seems like yesterday (perhaps due to the recent events in Afghanistan) and yet twenty years have passed since that Tuesday on September 11, 2001.

The attacks on that terrible day were a series of four coordinated suicide attacks against civilian and military targets in the United States of America by a group of terrorists belonging to the terrorist organization al Qaeda. The attacks caused the deaths of almost three thousand people (2977 to be precise), plus 19 hijackers and the injuries of over 6000. In the following years there were further deaths due to tumors and respiratory diseases linked to the consequences of the attacks: for these reasons and due to the huge infrastructural damage caused, these events are often considered to be the most serious terrorist attacks of the contemporary age.

That morning (local time, afternoon in Italy) four airliners belonging to two of the major US companies (United and American) were hijacked by 19 terrorists belonging to al Qaeda. Two aircraft (flight AA 11 and UA 175) were crashed into the North and South Towers of the World Trade Center, respectively, in the Lower Manhattan neighborhood of New York. Within an hour and 42 minutes both towers collapsed. The debris and fires then caused the partial or total collapse of all the other buildings in the WTC complex. A third aircraft, flight AA77, was crashed into the Pentagon, home of the Department of Defense, in Arlington County, Virginia; the attack caused the west facade of the building to collapse. A fourth plane, flight UA 93, was initially directed to Washington but later crashed in a field near Shanksville, Pennsylvania following a heroic passenger riot.

The destruction of the WTC damaged the Lower Manhattan economy and had a significant impact on global markets, even causing Wall Street to close until September 17. The removal of debris from the WTC site (later called "Ground Zero") was only completed in May 2002. Damage to the Pentagon was repaired within a year. On November 18, 2006, construction began on the One World Trade Center, which was inaugurated on November 3, 2014.