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What is the Pentagon?

Mary McMahon
Updated: May 17, 2024

The Pentagon is a building located in Arlington County, Va., near Washington, D.C. that houses the headquarters of the United States Department of Defense. The building has a unique pentagonal shape which surrounds an open courtyard, and houses 23,000 civilian and military employees. The Pentagon is often used as a symbol of the American military complex, as the shape makes it readily recognizable. The Pentagon is sometimes compared to a small city, due to the size and complexity of the building. It houses the Joint Chiefs of Staff and Secretary of Defense along with the Army, Navy, Air Force, and Marines.

The Pentagon's unique shape makes it a highly efficient office building. Although the Pentagon has 3,705,793 square feet (1,129,526 meters) of office space, it is possible to reach most points in the building within 10 minutes, a remarkable architectural achievement. In a building which coordinates the armed forces of the United States along with organizations responsible for intelligence and security, workers often need to be able to access each other quickly.

The idea of the Pentagon was conceived in 1941, when Brigadier General Brehon Sommervell was trying to solve the problem of limited space for the Department of Defense, a serious issue in the Second World War. It was agreed that a new building was needed, and a groundbreaking ceremony took place on 11 September, 1941. It took just two years to complete the building on former marshlands along the outskirts of Washington, and the Pentagon was quickly filled with communications equipment and staff to coordinate the Department of Defense.

Seventeen separate office buildings were consolidated in the Pentagon in order to make it a central location. The building has a large number of fixtures and amenities to supply the staff, including 284 bathrooms, 16,250 lighting fixtures, and 7,754 windows. The iconic building is available for tours, although access is restricted to certain areas and particular times. The Pentagon complex is on a 583 acre square area of land, which includes 67 acres of parking space for employees.

60 years to the day after the ground was broken for the Pentagon, American Airlines Flight 77 was hijacked and flown into the western side of the Pentagon, killing 189 people immediately upon impact. The Pentagon was evacuated, along with other major buildings in the area. Repairs on the site began quickly, with the space fully usable less than a year after the terrorist attacks.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a America Explained researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By bagley79 — On Apr 27, 2012

I wonder how many people they employ just to make sure the Pentagon is kept clean and maintained? Keeping almost 300 bathrooms clean is beyond the scope of my imagination.

My niece has made her career in the Navy, and she has very high security clearance. Her most recent job is working at the Pentagon. There is much about her work that she must keep confidential, but I enjoy hearing her talk about the massive, state-of-the art building she works in.

When she signed up for the Navy many years ago, she probably never dreamed she would one day have a Pentagon job.

By Mykol — On Apr 26, 2012

The Pentagon is certainly a huge building. Can you imagine 67 acres of parking just for the employees? I hope they have a good system to transport them from the parking lot to the building.

My office building is not nearly the size of this structure, and I think it takes longer than 10 minutes to reach some places in my building.

When I was in high school my family took a trip to Washington, D.C. We saw most of the familiar buildings and attractions, but we never made it to the Pentagon.

That is one place I hope to return to. When I do, I will make sure I get to take a tour of this huge place.

By SarahSon — On Apr 26, 2012

Of all the information I have read pertaining to the attack on September 11, 2001, I had never read about the connection between the Pentagon attack and the groundbreaking date of the Pentagon.

How sad when you realize how many lives were lost on that day. It is also amazing how quickly the building was able to be used again.

By ElizaBennett — On Apr 26, 2012
Something that not every realizes about the attack on the Pentagon on 9 11 is that it produced a whole lot of injuries as well as deaths. Few people, frankly, were injured in the World Trade Center attack, but it was a different story at the Pentagon.

Remember, the two kinds of damage were very different. Both towers of the World Trade Center collapsed completely, while the Pentagon was damaged, not demolished, and there was a lot of fire. So there were injuries and there were burn victims. I think maybe the reason they didn't get more press attention was that injured people didn't quite fit the narrative somehow. One of the few places that did give coverage to the Pentagon wounded was the Washington Post newspaper, since of course it was a local issue for them.

By anon216911 — On Sep 23, 2011

I'm working on how to target it.

By anon176087 — On May 14, 2011

yes, it is a very interesting, ironic fact.

By anon41702 — On Aug 17, 2009

I had no idea that the construction of the pentagon began on September 11th! That's eerie considering all the things that the numbers 9-1-1 brings!

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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