Pentagon History

Updated August 5, 2020 | Infoplease Staff

World's largest office building has distinctive past

by David Johnson
The Pentagon

The Defense Post Office handles 1,200,000 pieces of mail each month.

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The world's largest office building, the Pentagon is synonymous with the Department of Defense and a symbol of American military might.

Exactly 60 years before the September 2001 attacks, on September 11, 1941, ground was broken in Arlington Country, Virginia, for a huge new building to house the War Department, forerunner of today's Department of Defense. The department was then operating from 17 separate buildings in Washington.

Pearl Harbor Alters Plans

At certain periods 13,000 people worked on the project. Originally, plans called for three floors, but as the military prepared for war after the attack on Pearl Harbor, two more floors were added. To conserve steel, concrete ramps were used in place of elevators and the outside walls were made of reinforced concrete.

The Pentagon was built in "stripped classical" style, a variation of Greek and Roman classicism popular in the middle of the 20th century and often used for government buildings.

On January 15, 1943, just 16 months after construction began, the Pentagon was completed. In April, occupants began moving in. Including outside facilities, the project cost about $83,000,000.

Five Sides, Five Layers, Five Floors

Since five roads surrounded the site, builders chose a five-sided building, which is how the Pentagon got its name.

The building consists of five concentric rings connected by ten corridors that run, like spokes, from the inner ring to the outer. Interior courtyards that provide light separate the rings.

The corridors are a total of 17.5 miles long, while the building provides a gross floor area of 6,500,000 square feet. There are 3,800,000 square feet for offices, concessions, and storage. The five-sided center courtyard covers five acres.

A shopping concourse, numerous snack bars, cafeterias, dining rooms, banks, a subway station, and a bus platform make the Pentagon "a city within a city."

Massive Dimensions

The structure is supported by 41,492 concrete piles. There are five floors, plus mezzanines and basements. The building itself is 77 feet, 3.5 inches high. Each outside wall is 921 feet long.

More than seven acres of glass went into the 7,754 windows in the Pentagon. There are 16,250 light fixtures, with some 250 bulb replacements made each day. There are 7,000 electric clock outlets, 691 drinking fountains, 131 stairways, 19 escalators, 13 elevators, 672 firehouse cabinets, and 284 rest rooms.

The Pentagon site covers a total of 583 acres, while the building itself sits on 29 acres. The Pentagon's sewage treatment plant and the heating and refrigeration unit each cover one acre. The parking lot is 67 acres and has spaces for 8,770 vehicles.

Miles of Cables

Thirty miles of access highway and 21 bridges and overpasses were built to connect the complex to nearby roads.

Some 100,000 miles of telephone cable handle the 200,000 phone calls made at the Pentagon each day. The Defense Post Office handles 1,200,000 pieces of mail each month. At its peak during World War II, 33,000 people worked in the Pentagon.

A Historic Landmark

In 1992, the Pentagon became a national historic landmark. Architects noted the building's unusual shape, facades, courtyard, two terraces, and its history as significant characteristics.

September 11 Attack

In 1990, a major renovation plan was approved, calling for the building to be gutted, asbestos removed, and new plumbing, wiring, and other features installed in compliance with current building codes.

The plane that crashed into the Pentagon on September 11, 2001, hit a section that had recently been renovated and was still only partially occupied. Authorities say the death toll of 189 would have likely been much higher if the area had been fully occupied. The crash caused a gash on the west side of the Pentagon measuring 30 yards wide and 10 yards deep; 185,693 square feet were damaged and 37,161 square feet were destroyed. Three of the five Pentagon rings were damaged. It cost $501 million to repair the building; repairs were finished within a year of the attack.

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