PowerPoint Show by Andrew

Thirteen years ago, during the terrorist attacks of September 11, 2001, a passenger revolt against the hijackers of United Airlines Flight 93 resulted in the aircraft crashing into a field just outside Shanksville, Pennsylvania, killing all 44 people aboard (including the four hijackers).

Authorities believe this fourth hijacked aircraft was also to be used as a missile, targeting either the U.S. Capitol Building or the White House. In the years since, a national memorial at the Pennsylvania crash site has been under planning and construction, now due to be completed sometime in late 2015.

Phase one was completed in 2011, including the "wall of names," 40 granite slabs standing eight feet tall, inscribed with the names of the passengers and crew of Flight 93. On this 13th anniversary of that tragic day, here are a few recent images of the Flight 93 National Memorial.

Visitors walk along the wall of names of passengers on the eve of the 13th anniversary of the attacks at the Flight 93 National Memorial Visitor Center Complex in Shanksville, Pennsylvania, on September 10, 2014.

Candles in memory of the 40 passengers and crew of Flight 93, are carried to the Wall of Names at the Flight 93 National Memorial on Wednesday, September 10, 2014.

Yachiyo Kuge, the mother of Toshiya Kuge who was a passenger on Flight 93, places origami birds near his name, at the Wall of Names.

Navy Quartermaster Matthew Konchan, stands in a field of black-eyed Susan as he waits to participate in a wreath-laying ceremony.

Visitors gather at the boulder that marks the site of the crash of Flight 93.

Visitors to the Flight 93 National Memorial pause at the Wall of Names.

National Park Service lead a media tour of the Flight 93 Visitors Center Complex construction site on September 10, 2014.

A portion of the construction site at the Flight 93 Visitors Center Complex, photographed on Wednesday, September 10, 2014.

A visitor kisses a name on the Wall of Names.