A woman stands among some of the 3,000 flags placed in memory of the lives lost in the September 11, 2001 attacks, at a park in Winnetka, Illinois September 10, 2014. On Thursday people will mark the 13th anniversary of the 9/11 attacks.
A woman stands among some of the 3,000 flags placed in memory of the lives lost in the September 11, 2001 attacks, at a park in Winnetka, Illinois September 10, 2014. On Thursday people will mark the 13th anniversary of the 9/11 attacks. REUTERS/Jim Young

The year 2014 marks the 13th anniversary of the horrific attacks by al-Qaeda terrorists on the U.S. Memories of the day that saw thousands of deaths and injuries and loss of pivotal infrastructure will always remain engraved in the hearts of Americans. Sept. 11, 2001 was one of the saddest days in the history of the world. On Thursday, the world will remember the day that changed the life of millions. Here are some facts about 9/11 attacks that everyone should know.

1. On Sept. 11, 2001 America was rocked by a series of four terrorists attack planned and implemented by one of the biggest terrorists group called al-Qaeda. The attack was executed by 19 militants using four hijacked aircrafts in the two American metropolitans, New York City and Washington D.C.

2. The nature of terrorists attacks were suicide attacks using passenger airplanes that were dashed into the two significant business centers in America. Two planes were flown into the World Trade Center in Manhattan and the third one bumped off in the Pentagon in Washington and the fourth one fell in Shanskville in Pennsylvania.

3. The first strike was made by American Airlines Flight 11 at north tower of the World Trade Center at 8:46 a.m. Within 15 minutes, the second attack took place and at 9:03 a.m. United Airlines flight 175 hit the south tower of World Trade Center. At 9:37 a.m. the third strike was made at Pentagon Building by American Airlines Flight 77.

4. Al-Qaeda was the prime suspect for the 9/11 attacks and it was later confirmed when their leader Osama Bin Laden took the responsibility of the attack in a video. The terrorist organization even stated their motives behind the attack on the U.S. It is said that the attacks were act of protest and revenge on the U.S. government that supported Israel. Also, presence of the U.S.A. military forces in the Middle East was one of the reasons of the attack.

5. 9/11 attack took the lives of 2996 people. The number included 19 terrorists and 2977 civilians. As for the damage of infrastructure, 110 storey World Trade Center, Pentagon Building and other buildings such as St. Nicholas Greek Orthodox Church, Marriott Hotel and Deutsche Bank Building.

6. Following the 9/11 attacks, several memorial services and vigils are held in and around America. Sept. 11 is observed as Patriot Day, the day when they remember those who lost their lives in the attack. This day is also called National Day of Service and Remembrance. Each year, the flag of America is flown at half-mast on all the government buildings in the U.S. including White House. Also, a moment of silence is observed in the remembrance of the deceased.