Pentagon

From 9/11 Encyclopedia:

The Pentagon--a building, institution, and symbol--was conceived at the request of Brigadier General Brehon B. Sommervell, Chief of the Construction Division of the Office of the Quartermaster General, on a weekend in mid-July 1941. The groundbreaking ceremony took place on September 11, 1941. The first occupants moved in 29 April 1942. Height of building (ft.) 77' 3.5" 
Source: http://www.defenselink.mil/pubs/pentagon/facts.html

The Pentagon was one of the safest buildings in the world for 60 years until it was attacked on September 11th, 2001 at exactly the same part, which was just renovated. (See Controlled Cleanup) There was no explanation as why the building wasn't evacuated, when the Twin Towers got hit and 2 planes still got hijacked. (See Clarke,Veronica) Compare: All Pentagon-links on attack of September 11th 
http://www.defenselink.mil/pubs/pentagon/pentagoninfo.html

'Black Boxes' Found at Pentagon Crash Site http://www.defenselink.mil/news/Sep2001/n09142001_200109142.html 

Alleged Terrorist Airliner Attack Targets Pentagon http://www.defenselink.mil/news/Sep2001/n09112001_200109111.html 

Myers and September 11: "We Hadn't Thought About This" http://www.defenselink.mil/news/Oct2001/n10232001_200110236.html

(-> Pentagon, simulated Crash) (See Tricare Exercise) (See Pentagon-Collapse) 
(See Pentagon-Crash) (-> Pentagon-Hole) (See Pentagon, Missing Money) Pentagon-Warning September 10th