The corridors of the Pentagon are nearly 18 miles long, with 66 million square feet of space. It's one of the largest buildings in the world, larger than the Empire State Building.
The design of Washington D.C.'s flag was based on the shield from George Washington's family coat of arms.
Don Wildman: Washington D.C. is the capital of the most powerful nation on Earth. As a result it's among the most tightly secured cities on the planet and since 9/11 security here has only gotten tighter. For 200 years when it's come to defending the nation's seat of power has been to go underground. From a tightly guarded maze of tunnels beneath the heart of the nation's capital to a recently declassified super-bunker below the mountains of West Virginia where the nations leaders could survive nuclear armageddon and General Robert E. Lee's subterranean weapons factory hidden in a cave right below a Union Army camp.