The Pentagon (in English: The Pentagon) is the headquarters of the United States Department of Defense, located in Arlington County, Virginia, near Washington, D.C. The building is shaped like a pentagon and employs approximately 23,000 military and civilian employees,[1]​ and nearly 3,000 support personnel. It has twelve floors, five of which include five corridors; the rest is unknown. Construction of the Pentagon began on September 11, 1941, shortly before the United States entered World War II, and it was inaugurated on January 15, 1943. It was for decades the largest office building in the world until in 2023 it was surpassed by the Surat Diamond Exchange in India.[2][3]​.

The Pentagon owns between 700 and 800 bases in sixty-three countries, with a total area of ​​120,191 square meters.[4] Statistics from 2006 show that the Army controls the majority of Department of Defense properties (52%), followed by the Air Force (33%), the Marine Corps (8%), and the Navy (7%).[5]

The Pentagon includes twice as many bathrooms as necessary, because at the time of construction there was a law that required the existence of one bathroom for whites and another for blacks.[6] It also has facilities for eating and exercising, as well as meditation and prayer rooms. Visits for the public were suspended after the attacks of September 11, 2001.

The architects and designers came up with a unique pentagonal plan for the building to maximize the strange dimensions of the site and fit the expanse of land.

On September 11, 2001, exactly the day that marked sixty years since the beginning of its construction, a team of five Al Qaeda hijackers took control of American Airlines Flight 77, en route from Washington-Dulles International Airport to Los Angeles International Airport and deliberately crashed it into the Pentagon at 9:37 in the morning, as part of the September 11 attacks. All 64 people on the passenger plane died, as well as 125 people who were in the building. The impact of the plane severely damaged the structure of the building and caused its partial collapse. At the time of the attacks, the Pentagon was undergoing renovations and several offices were unoccupied, resulting in fewer casualties. Contractors already assisting with the renovation were given the additional task of rebuilding sections damaged in the attacks. This additional project was named and was responsible for the restoration of peripheral offices damaged by the attack of September 11, 2001. After the incident, the staff resumed their work as of August 15, 2002.