The Pentagon

The Pentagon is the headquarters for the United States Department of Defense. It is located in Arlington County, Virginia, across the Potomac River from Washington, D.C. Because it is the center of military leadership, people often use the name "The Pentagon" to refer to the entire Department of Defense.

The building is the second-largest office building in the world. It spans a massive area and includes a large central courtyard. The structure has five sides and five floors above the ground. There are also two basement levels. The building's design uses five concentric rings of corridors on each floor. These rings are named "A" through "E" starting from the center. The basement also contains "F" and "G" rings.

Navigating the building is a unique experience. The corridors radiate out from the central courtyard. The "E" Ring is the outermost ring and is the only one with views of the outside. Because of this, senior officials often occupy these offices. Office numbers follow a specific system based on floor, ring, and corridor. For example, an office number might include the floor and the ring letter. Despite its enormous size, a person can walk between any two points in less than ten minutes. This is possible by using the radial corridors or walking through the open-air courtyard.

Before the Pentagon was built, the War Department faced a major space problem. Its offices were scattered across many temporary buildings in Washington, D.C., Maryland, and Virginia.

Some of these structures were located on the National Mall. As World War II approached, Secretary of War Henry L. Stimson realized the department needed a single headquarters. In 1941, General Brehon Somervell helped create a plan for a new building. The project was overseen by the U.S. Army Corps of Engineers under Colonel Leslie Groves.

Construction began on September 11, 1941, and was completed on January 15, 1943. The project moved on an accelerated schedule due to the war. The building was designed by architect George Bergstrom and built by contractor John McShain. To save steel for war needs, engineers used reinforced concrete instead. They used 680,000 tons of sand dredged from the Potomac River to make the concrete. The total cost for the construction was approximately $83 million. The building was constructed in sections, or "wedges," so people could move in as soon as parts were finished.

The Pentagon is a very busy place. Today, about 23,000 military and civilian employees work inside the building. There are also about 3,000 non-defense support personnel on site. The building has several entrances, such as the River Entrance and the Concourse. It is so large and important that it has six different ZIP codes. These codes are divided among the Secretary of Defense, the Joint Chiefs of Staff, and the four military service branches.

History also includes a very difficult period for the building. On September 11, 2001, American Airlines Flight 77 struck the western side of the Pentagon. This attack killed 184 people, including 59 people on the airplane and 125 people inside the building.

This was the first major foreign attack on federal facilities in the capital area since the War of 1812. After the damage was repaired, a small indoor memorial and a chapel were added at the site of the impact. In 2009, an outdoor memorial was opened southwest of the building to honor the victims.