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Pentagon History: 7 Big Things to Know

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The Pentagon is a universal symbol of U.S. strength and security known around the world, but do you know the history behind it?

The 1,100 acres of land on which the Pentagon sits was once part of the sprawling estate of Confederate Gen. Robert E. Lee. The federal government confiscated it during the Civil War, but the building's concept and construction didn't happen until several decades later.

Here's the rest, in a nutshell.

It was supposed to be temporary.

The Pentagon was the brainchild of Army Brig. Gen. Brehon B. Sommervell, who, in the early 1940s, pitched it as a temporary solution to the then-War Department's critical shortage of space as the threat of joining World War II became imminent.

The plan was approved, and on Sept. 11, 1941, construction began. About 296 acres of land were designated for the building, which was supposed to be turned into a hospital, office or warehouse once World War II was over.

Construction begins on a massive plot of land. In the distance is the Washington Monument.
Pentagon View
The first side of the Pentagon begins to take shape on a plot of land in Arlington, Va., across the Potomac River from the Washington Monument, Nov. 5, 1941.
Photo By: DOD
VIRIN: 411105-D-ZZ999-919C
An aerial view of two sides of the Pentagon that are nearly complete during its construction. The Washington Monument and Potomac River are visible in the distance.
Pentagon Construction
An aerial view of the Pentagon’s construction, Feb. 29, 1942.
Photo By: DOD
VIRIN: 420301-D-ZZ999-833C
Four of the five sides of the Pentagon building are visible on a massive plot of land that’s under construction.
The Five Side
Four of the five sides of the Pentagon come into shape during the building’s construction, April 18, 1942.
Photo By: DOD
VIRIN: 420418-D-ZZ999-998C

Why make it a pentagon shape?

The logic behind this was pretty simple — the site designated for construction was bordered by five roadways, so the developers decided to go with a five-sided building. Naturally, they called it the Pentagon.

An incredible amount of workers and materials brought it together.

The grounds and building went up in a stunning 16 months. The building was officially completed in January 1943, thanks to the help of 1,000 architects and 14,000 tradesmen who worked three shifts around the clock. A staggering amount of materials were needed, too, including:

  • 435,000 yards of concrete
  • 43,000 tons of steel
  • 680,000 tons of sand and gravel

The first tenants moved into the building in April 1942, several months before the building was finished.

Scaffolding, a crane and construction crews surround a building that will eventually be the Pentagon.
Construction Crew
The Pentagon’s facade nearing completion, Dec. 21, 1942.
Photo By: DOD
VIRIN: 421221-D-ZZ999-722C

Temporary needs quickly became permanent.

At the height of World War II, the Pentagon housed more than 33,000 people, and its worth exceeded expectations. Officials discovered that they did, in fact, need to keep such a large military force active once the war was over. So, instead of turning the building into something else, it remained the military's command center.

Nowadays, it houses the Office of the Secretary of Defense, the Joint Chiefs of Staff and the highest echelons of the Army, Navy, Marine Corps and Air Force.

In 1992, the building was designated a National Historic Landmark. Due to its age, renovations began around that time on the building's 4 million square feet of space.

An aerial view of the charred and partially collapsed Pentagon, with fire trucks and emergency crews working around rubble.
Destruction View
An Aerial view of the destruction at the Pentagon caused by a hijacked commercial jet that crashed into the side of the building during the Sept. 11, 2001, terror attacks
Photo By: Air Force Tech. Sgt. Cedric H. Rudisill
VIRIN: 010914-F-8006R-003C

Ongoing renovations likely saved lives on 9/11.

On Sept. 11, 2001, the nation's sense of security was shattered when terrorists hijacked commercial airplanes and flew them into New York City's World Trade Center, into a field in rural Pennsylvania, and into the nation's symbol of military might.

American Airlines Flight 77 crashed into the west side of the Pentagon, penetrating three of its five rings and killing 184 people. Thankfully, several offices in that area weren't occupied because of the ongoing renovations. In fact, one of the sections had just finished getting upgrades that improved security features, including walls and windows with greater blast resistance. An initial analysis after the attacks suggested that helped to save a lot of lives.

Construction crews work on floors and walls at the Pentagon
Pentagon Reconstruction
Reconstruction of the Pentagon continues nearly around the clock as work crews pour cement for floors and walls, Feb. 6, 2002, to replace those damaged in the 9/11 terrorist attack on the building.
Photo By: Grant Greenwalt
VIRIN: 020206-D-0000G-004

Post-9/11 renovations continued for a decade.

The team working those initial renovations was tasked with rebuilding the damaged portions. The reconstruction effort was dubbed the Phoenix Project, and it cost $500 million.

By Aug. 15, 2002 — less than a year later — the first tenants whose offices were damaged began to return, even though renovations were nowhere near complete.

Aside from the rebuild, a groundbreaking for a memorial honoring the lives of the 184 killed at the Pentagon on 9/11 began June 15, 2006. The memorial, which was dedicated on Sept. 11, 2008, sits on a two-acre plot of land on the southwest side of the building, next to where the airplane struck that fateful day.

A man sits at one bench in a field of benches.
Bench Reflection
Philadelphia 76ers point guard Vasilije Micic reflects at a bench during a team tour of the National 9/11 Pentagon Memorial, Oct. 12, 2016.
Photo By: Marvin Lynchard, DOD
VIRIN: 161012-D-FW736-014C

There were challenges.

Even before the terrorist attacks, the renovations were considered a massive undertaking, which included:

  • Removing all hazardous materials
  • Replacing all building systems
  • Adding new elevators and escalators to improve vertical circulation
  • Installing new security and telecommunications systems to match the times
  • Integrating sustainable design measures and force protection initiatives prompted by the 9/11 attacks
  • Environmental considerations: High-efficiency lights, recycled gypsum wall board and recycled-content carpet were installed, and 90 percent of all the concrete and metal used was diverted from landfills

According to Pentagon historians, 40,000 personnel had to be relocated during the project's various phases, which went as follows: Each wedge was broken into 10,000 square feet; plumbers, electricians and other tradesmen then had five days to complete their tasks before moving onto the next 10,000 square-foot section.

The first section was completed in 26 weeks to accommodate a timetable laid out by Congress.

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