At left, smoke billows out from the Southwest E-ring of the Pentagon on September 11, 2001 in Arlington, V.A., after American Airlines Flight 77 crashed into the building and set off a huge explosion. (Photo by Alex Wong/Getty Images.) At right, a temporary memorial rests at the crash site of the Flight 93 National Memorial in Shanksville, Pennsylvania, on September 11, 2010, during a service of remembrance marking the 9th anniversary of the 9/11 attacks. (Jim Watson/AFP via Getty Images.)
