The construction of The Pentagon in Arlington, VA was started on September 11, 1941 ... exactly 60 years before American Airlines flight 77 struck the building on the historic day of the 911 attacks on 9/11/01. The Pentagon houses the US Department of Defense and is shaped like a pentagon if you see it from the sky. I have always found it odd that such an important building was so distinguishable from the sky. It was designed this way to help it fit into the ridge where it was originally planned. President Roosevelt moved it from that ridge to its current site because he didn't want it to obstruct the view of DC from Arlington Cemetery. The design remained after they changed the site of the project.
The cafe in the center of the building is called ... The Ground Zero Cafe. This was named long before 911.
The Pentagon is so large that you could fit 3 Empire State Buildings in it.
This building was started just 3 month before we were attacked at Pearl Harbor. At that point, the President knew that the War was inevitable. He knew the building would be needed but thought they would never fill it so had planned on using parts of the building as a library. Ironically, this is one of the reasons why the attacks on the building in 2001 did so little damage. The floors of the building are irregularly thick, thick enough to hold the weight of a ton of books.