The Pentagon is the headquarters of the United States Department of Defense. It is in Arlington, Virginia (near Washington, D.C.). It has limestone walls. It is in the shape of a pentagon, and has seven floors.

The Pentagon is the largest office building in the world,but any place in the building can be reached within 7 minutes.

Construction began on September 11, 1941. Exactly sixty years later, on September 11, 2001, it was hit with an airplane by terrorists. The crash killed a total of 189 victims (125 in The Pentagon, 64 in plane).

Building description
It has a total floor area of 6,500,000 sq ft (604,000 m2). Offices are 3,700,000 sq ft (344,000 m2). Approximately 25,000 military and civilian employees work in The Pentagon.  It has five sides, five floors above ground, two basement levels, and five ring corridors per floor with a total of  of corridors. The Pentagon includes a five-acre (20,000 m2) central plaza, which is shaped like a pentagon.

The concentric rings are named (from the center out) as "A" through "E" (with in addition "F" and "G" in the basement). "E" Ring offices are the only ones with outside views and are generally occupied by senior officials. Office numbers go clockwise around each of the rings, and have two parts: a nearest-corridor number (1 to 10) followed by a bay number (00 to 99), so office numbers range from 100 to 1099. These corridors radiate out from the central courtyard, with corridor 1 beginning with the Concourse's south end. Each numbered radial corridor intersects with the corresponding numbered group of offices (for example, corridor 5 divides the 500 series office block). There are a number of historical displays in the building, particularly in the "A" and "E" rings.

Floors in The Pentagon are lettered "B" for Basement and "M" for Mezzanine, both of which are below ground level. The concourse is located on the second floor at the metro entrance. Above ground floors are numbered 1 to 5. Room numbers are given as the floor, concentric ring, and office number (which is in turn the nearest corridor number followed by the bay number). So, office 2B315 is on the second floor, B ring, and nearest to corridor 3 (between corridors 2 and 3). One way to get to this office would be to go to the second floor, get to the A (innermost) ring, go to and take corridor 3, and then turn left on ring B to get to bay 15.

Just south of The Pentagon are Pentagon City and Crystal City, extensive shopping and high-density residential districts in Arlington. Arlington National Cemetery is to the north. The Washington Metro Pentagon station is also located at the Pentagon, on the Blue and Yellow Lines. The Pentagon is surrounded by the Capital Beltway Every day, thousands of commuters traveling between Arlington, Virginia and Washington, DC drive on the roads of the Pentagon Reservation.

The Pentagon Athletic Center (PAC) is a fitness center for military and civilian staff. It opened in a separate building on the north side of The Pentagon in 2004. Each year, the Pentagon grounds hold the Marine Corps Marathon and the Army Ten-Miler running events.

The public may take a 60 minute long tour of the building. Tourists can also visit the Pentagon Memorial that is on the building's west side.The Pentagon receives around 106,000 visitors per year.

Some numbers about The Pentagon 
The Pentagon has:
 131 stairs
 19 escalators
 70 elevators 
 7,754 windows 
 284 toilets
 691 water fountains
 4,200 clocks
 16,250 lights
 17.5 miles of corridor
 200,000 telephone calls per day
 1,000,000 emails sent daily
 8,700 parking spaces

9/11 Attacks 
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.

References

Other websites 

 The Pentagon website 

 
September 11 attacks
1943 establishments in the United States
1940s establishments in Virginia