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As the nerve center of the United States Department of Defense, this massive structure serves as both a fortress and a hub of military strategy. Did you know the Pentagon was built in just 16 months during World War II? Or that it has over 17 miles of corridors, yet the walk between the two furthest points takes only about seven minutes?
With service tunnels running beneath it, a classified command center at its heart, and its own stop on the Washington Metro, the Pentagon is full of mystery. But what really goes on behind its walls? Who gets access to its top-secret rooms? And what makes it one of the most impenetrable buildings on Earth?
The world’s biggest low-rise office building, the Pentagon is perhaps one of the most iconic military structures in the United States, and for good reason. In fact, it is so large that it has its own zip codes. Six of them, as a matter of fact.
The idea for the Pentagon crystallized on a single day, July 17, 1941, when, at a House Appropriations subcommittee hearing, Chairman Clifton Woodrum pressed the War Department for an overall answer to its space problem, and Brigadier General Brehon Somervell, whose department was already scattered across seventeen buildings in Washington and bursting out of a headquarters that had only just been finished, seized the moment and ordered his designers to draw up plans for one building big enough to hold all of it.
Congress moved with startling speed. The House approved the project on July 28, 1941, and the Senate followed on August 14, four weeks after Somervell first floated the idea.
The site chosen for the new building was a plot of land in Arlington, Virginia, just across the Potomac River from Washington, DC. Construction began on September 11, 1941, just months before the United States entered World War II. The building was completed in just 16 months, an impressive feat given the project's size and complexity.
But why is the Pentagon we know named the Pentagon? Under pressure from Congress to find a permanent solution to the department's space problem, the military turned to the head of the Army's Construction Division, tasking the chief of the design section with fitting a building onto a rough five-sided parcel just below Arlington National Cemetery – land the government had owned since buying the Custis-Lee estate in 1883, and which Congress had handed back to the War Department in November 1940.
To take advantage of the site's unusual dimensions, the architects and designers developed a distinctive pentagonal concept for the structure. The first draft had just two concentric rings of office space wrapped around a huge central court. The five concentric rings we know today, later labeled A through E, and stitched together by ten corridors radiating out from the courtyard like spokes on a wheel, wouldn't be settled until September, and only after the whole project had been picked up and dropped somewhere else entirely. Which is a story in itself.
President Franklin D. Roosevelt, however, decided the new headquarters should instead be built on the site it occupies today, at the foot of the Virginia side of the 14th Street bridge over the Potomac.
The decision was made right after the chairmen of the Commission of Fine Arts and the National Capital Park and Planning Commission protested that the building would wreck the view of Washington from Arlington Cemetery. When Somervell kept pressing for the cemetery site during a tour of both locations, Roosevelt cut him off: "My dear General, I'm still Commander-in-Chief of the Army."
The design concept, and hence, the Pentagon name, were kept.
The new site was low-lying ground known as "Hell's Bottom," a run-down stretch of shacks, dumping grounds, warehouses, and rail yards that the War Department had actually fought against, calling it unworthy of the department's dignity. Clearing it meant condemning as many as 150 homes, whose families were given very short notice to move.
The land came from three main holdings. 80 acres of the Arlington Cantonment at Fort Myer that had been earmarked for a Quartermaster depot, 146.5 acres of the former Washington-Hoover Airport, and 57 acres off the southern end of Arlington Farms. But by the time the road network was accounted for, the government had assembled 583 acres in more than 160 separate parcels.
The building was finished in January 1943 with a gross floor area of about 6.24 million square feet (closer to 6.5 million today), and it remains the world's largest low-rise office building as of September 2026.
During construction, the builders conserved enough steel to build a battleship. And the 680,000 tons of sand and gravel used to make the building's reinforced concrete were dredged straight out of the neighboring arm of the Potomac and barged to an on-site batching plant, where they became 435,000 cubic yards of concrete.
But the speed cost money. Initially budgeted at $35 million, the final cost was $83 million, which works out to roughly $1.6 billion in 2026 money. With all the massive reconstruction it has undergone, the building boasts 7,754 windows and 17.5 miles of corridors. Five rings, five stories above ground, and two floors below ground make up the well-known structure. From the inside courtyard to the exterior, the rings are designated "A" through "E."
The most senior officials' offices are on the E-ring because it is the only one with outside views. Yet, its bespoke design means it takes only about 7 minutes to walk between the furthest two points in the building.
The building has five main façade entrances, and every room carries a code that pins down its location exactly. The Secretary of Defense's office, 3E880, is on the third floor, in the E ring, off corridor 8, office bay 80. The system has barely changed since the 1940s.
A construction of this size needed someone at the top who could keep the whole thing moving. On August 19, 1941, Army Corps of Engineers Colonel Leslie Groves was brought in to oversee the Pentagon project, though he was also running the Army's construction program nationwide. The officer who actually directed the contractors day-to-day on site was the district engineer, Clarence Renshaw.
Groves was in his Washington office six days a week. He would then go on Sundays to the project he thought needed his personal attention most. Groves had a reputation for being a strict boss, and one of his deputies, Robert Furman, was required to be at the Pentagon day and night. Furman had the Pentagon contractors construct a secret apartment between the walls so he could sleep. Furman kept using the apartment on official trips back to Washington even after he moved on to the Manhattan Project as an intelligence officer – until 1943, when ordnance officers caught him coming out of it and made him hand over the keys.
During World War II, messengers traveled the hallways by bike or roller skates. As time went on, electric vehicles were added to the mix – a big mistake, as it caused damage to the building’s interior and chaos for those on foot. In the 1960s, the Secretary of the Air Force, Eugene Zuckert, was struck by a vehicle in a hallway intersection near his office. Today, electric scooters are available only for those who cannot get around on their own.
The Pentagon's planners had to design the building with separate facilities for black and white employees in a highly segregated America. These facilities included 284 bathrooms, twice as many as were required for the expected staff levels, and segregated cafeterias for the construction crews. However, Executive Order 8802, signed by Roosevelt in June 1941, barred discrimination in hiring across the federal government and its contractors.
But the legal basis for segregating the building fell away on March 11, 1942, when Virginia's governor, Colgate Darden, granted Secretary of War Stimson's request for exclusive federal jurisdiction over the land on which the Pentagon was being built. Even then, the Army kept preparing separate facilities anyway. The extra washrooms were built. The 'White' and 'Colored' signs never were. Most likely because Roosevelt, who toured the half-finished building with Harry Hopkins, demanded to know why there was such an extravagance of lavatory space.
The Pentagon has a shopping mall, a post office, medical facilities, dry cleaners, a barbershop, and multiple dining options, making it function almost like a self-contained city.
You may also be surprised that for most of its life the Pentagon had exactly one passenger elevator, and it was reserved for the defense secretary. Passenger lifts arrived only with the renovation program, which rebuilt the building wedge by wedge. The first wedge came within five days of completion in September 2001, before the attack forced much of it to be torn out and rebuilt. The last was finished in 2011. Before the renovation, anyone who couldn't manage the stairs used the building's long interior ramps. The Pentagon was built with freight elevators, which others used when needed.
As the headquarters of the Department of Defense (Department of War), inside the building, the most sensitive conversations happen in sealed rooms called SCIFs, built to a federal standard that can require radio-frequency shielding in the walls, floors, and ceilings so that no signal and no stray electronic emission from a screen or a cable ever leaves the room.
The Pentagon was never built to survive an attack. It went up as a conventional reinforced-concrete office block, deliberately light on steel because steel was needed for ships and tanks, and although Roosevelt pressed for a windowless building to make it less vulnerable to air raids, his engineers talked him out of it as impractical, and no blast protection was ever engineered into the structure.
Blast protection was retrofitted from the 1990s onward – structural steel framing behind the outer walls, a Kevlar-type mesh to catch flying debris, and blast-resistant windows weighing well over a thousand pounds each. Only one wedge had received it by September 2001.
And they came close to building a second Pentagon deep under Washington. In 1962, the Pentagon proposed the Deep Underground Command Center – a bunker three to four thousand feet beneath the Washington area, hardened to survive direct hits from multi-megaton weapons and to hold the president and a few hundred staff for a month after an attack. Congress refused to fund it, McNamara let it drop in 1966, and it was never built.
While the end of the world wasn’t on the way, one tragedy shook the world, and the Pentagon building was right in the line of fire. On September 11, 2001, the Pentagon was about one-fifth of the way through its first full-scale renovation when American Airlines Flight 77 crashed into the building's west face, between corridors 4 and 5 of Wedge 1, tearing through the outer three rings.
The Boeing 757-200 aircraft was hijacked by terrorists as part of the September 11 attacks, deliberately aiming at the building. 184 people lost their lives. The toll would almost certainly have been worse anywhere else in the building. Wedge 1 was the only section that had received the blast upgrades, and the engineers who investigated afterward found that the new blast-resistant windows almost all held. But it was the building's original 1940s frame, its spirally reinforced columns, continuous floor reinforcement, and short spans, that carried the load for about twenty minutes and gave people time to get out before a section above the impact came down.
Soon after, planners established a massive rehabilitation program known as the Phoenix Project. Originally estimated at $740 million, it came in at around $501 million, and by February 2003, every area damaged in the attack had been rebuilt and reoccupied.
Beyond the reconstruction, ground was broken in 2006 for a national memorial honoring the 184 lives lost at the Pentagon.
As part of the Pentagon’s rebuilding after the 9/11 attacks, a time capsule was placed inside the newly reconstructed section, commemorating the attack and recovery efforts. It holds a plaque with the names of the 184 victims and is sealed with special items. Two cards handmade by students representing the thousands of cards sent to the Pentagon after the attacks. A book of names from people across the country thanking members of the military. Patches from the Arlington County Fire and Police and a photo signed by the president depicting Defense Secretary Donald Rumsfeld and President Bush at the Pentagon shortly after the attack.
But the one spot in the building most tangled up in rumor is gone. In the middle of the Pentagon's five-acre courtyard there used to be a tiny hot dog stand – the third eatery to occupy that patch of ground, put up in the late 1980s. It was torn down in 2006 and replaced with a $1.2 million café, and because the courtyard is one of five historically protected features of a National Historic Landmark, the replacement had to be roughly the same size and exactly the same shape - a pentagon. Even the wooden owl on the roof, there to scare off birds, had to be preserved and put back. Today the courtyard eatery is a Potbelly, which opened in the summer of 2024.
The Pentagon can feed a workforce the size of a small town without anyone ever leaving the building. With more than twenty restaurants inside, the Pentagon has a bustling culinary scene that serves its vast workforce. The layout features three main food courts, a scattering of single-unit cafés, and a rotating cast of pop-ups that changes every weekday. These offer a wide range of recognizable options, including McDonald's, Subway, Taco Bell, Panda Express, Popeyes, Panera Bread, and Starbucks.
The Pentagon is connected to the Washington Metro system, with the Pentagon Metro Station serving the building since 1977. The Pentagon also has an extensive network of tunnels for logistics and maintenance, but these are not a classified transportation system.
Today, the Pentagon still houses the offices of top military leaders and serves as the Department of Defense's nerve center.
More than 100,000 people visit the Pentagon each year. A 60-minute guided tour highlights the building's history and the Department of Defense. Covering approximately 1.5 miles, the guided tour includes the Hall of Heroes, which honors America’s Medal of Honor recipients, as well as an exhibit dedicated to prisoners of war and those missing in action.
Outside, on the west side of the building where Flight 77 came in, is the National 9/11 Pentagon Memorial, a two-acre park with 184 illuminated benches, one for every victim. It isn't part of the indoor tour; it's open to the public every day of the year, and it is the only place on the Pentagon grounds where you're allowed to take a photograph.
The Pentagon remains a symbol of American values, ideals, strength, and determination in the face of adversity.
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