The Pentagon
On September 11, 2001, American Airlines Flight 77 flew into the western side of the Pentagon. September 11 was also the date the Pentagon began to be constructed. There were much fewer deaths because that side was being renovated. 189 people died. There is now a memorial remembering the people who died that day called the Pentagon Memorial.  Each person that died is represented by a bench, for a total of 189 benches. It was opened on September 11, 2008, exactly 7 years after the attacks.