The Pentagon Memorial, located just southwest of The Pentagon

The Pentagon

The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia. As a symbol of the U.S. military, "the Pentagon" is often used metonymically to refer to the Department of Defense rather than the building itself.Designed by the American architect...

 in Arlington County, Virginia

Arlington County, Virginia

Arlington County is a county in the Commonwealth of Virginia. The land that became Arlington was originally donated by Virginia to the United States government to form part of the new federal capital district. On February 27, 1801, the United States Congress organized the area as a subdivision of...

, is a permanent outdoor memorial to the 184 men and women who lost their lives as victims of the attack, killed both in the building and on American Airlines Flight 77

American Airlines Flight 77

American Airlines Flight 77 was American Airlines' daily scheduled morning transcontinental flight, from Washington Dulles International Airport, in Dulles, Virginia to Los Angeles International Airport in Los Angeles, California...

 in the September 11, 2001 attacks.

Designed by Julie Beckman and Keith Kaseman of the architectural firm of Kaseman Beckman Advanced Strategies

Kaseman Beckman Advanced Strategies

Kaseman Beckman Advanced Strategies is a design and architecture firm founded in 2002 and based in Philadelphia, Pennsylvania.Its principals are Julie Beckman and Keith Kaseman...

 with engineers Buro Happold

Buro Happold

Buro Happold is a professional services firm providing engineering consultancy, design, planning, project management and consulting services for all aspects of buildings, infrastructure and the environment, with its head office in Bath, Somerset...

, the memorial opened to the public on September 11, 2008.
In the aftermath of the 9/11 attacks, an impromptu memorial was set up on a hill at the Navy Annex, overlooking the Pentagon.