Those of you wondering just why the Pentagon is shaped like, well, a pentagon, need wonder no more. In a nutshell: they needed a huge building, which for political-aesthetic reasons couldn't be tall. The Northern Virginia lot chosen was roughly pentagon-shaped, so that defined the building. A different non-pentagonal site was then chosen, but since everyone was in such a goddamned hurry, the shape was never changed. Bureaucratic Murphy's Law-ism at it's best!