The Pentagon

A fire truck sits in front of the damaged area of the Pentagon Building outside of Washington, September 12, 2001. Photo: © REUTERS/Larry Downing

Since World War II, the Pentagon has stood as the headquarters and symbol of Americaís military might. The five-sided building houses military personnel and civilians working for each of the five branches of the armed services - Army, Navy, Marines, Air Force and Coast Guard - and symbolizes their unity in defense and war.

Satellite image of the Pentagon September 12, 2001, showing damage (Top Right). Photo: © REUTERS

In the early 1940s, the Pentagon Building was conceived by Brigadier General Brehon Sommervell to provide a solution to the War Departmentís shortage of space. The hope was that by consolidating the 17 buildings of the War Department, the speed of communication would improve.

Located in Arlington, Va., on the Potomac River across from Washington, the Pentagon is one of the worldís largest office buildings. With 3.7 million square feet of office space, the Pentagon has three times the floor space as the Empire State Building. Despite its size, the Pentagon is dwarfed by the total office space lost in the destruction of the World Trade Center towers and surrounding buildings. The attack wiped out 17.8 million square feet of space in Manhattan.

Offices inside the Pentagon building are arranged in five concentric rings, named A to E, from the inside ring out. In the center is a courtyard. Ten corridors link the rings like spokes on a wheel. Despite 17.5 miles of corridors, it takes only seven minutes to walk between any two points in the building, according to the Department of Defense.

The Boeing 757 airliner that crashed into the Pentagon on Sept. 11 was flying at full power and was steered directly into the southwest side of the building, between the first and second floors, opposite a helipad. Some of the area demolished was unoccupied due to a renovation, keeping fatalities lower than they might have otherwise been. Roughly 23,000 people work at the Pentagon. The Department of Defense said that 188 people are unaccounted for and presumed dead, including 64 people on the airplane.

Only the outer, very exposed ring has collapsed, though there is damage to two outer rings on each side of the crash site and to some covered walkways. There is also concern that the large amounts of water used to put out stubborn fires may cause flood damage to the structure.

In its day, the plan to build the Pentagon at the site of Arlington Farms was controversial. President Franklin D. Roosevelt vacillated about it. Critics said the huge office building would be hurriedly built and would be an eyesore, diminishing the beauty of the Washington skyline. The original plan, to appease such critics, was for a 3-story building that would not compete with monuments and other federal buildings. The final building is five stories high plus a mezzanine and a basement.

Construction began exactly 60 years before the terrorist attack - September 11, 1941 - and the Pentagon was dedicated in January 1943.

The attack on Pearl Harbor on Dec. 7, 1941, had a big impact on the speed of construction, putting to rest squabbles among politicians.

The building was made by dredging the nearby Potomac River for 680,000 tons of sand and gravel and mixing it with cement to make 435,000 cubic yards of concrete that was poured into forms to support the structure, according to the American Society of Civil Engineers. The interior walls are a more-expensive architectural concrete, and the outside is faced with limestone, not marble.

Arlington County, Va., Fire chief Ed Plaugher, called the building, ìvery, very stoutÖa lot of concrete, a lot of very thick masonry.î On top of that is a wooden roof structure and a slate roof, he said. The type of construction has made it a ìvery, very difficult system to get through to extinguishî for firefighters.