Pentagon column reinforcement bar
This piece of coiled reinforcement bar from a concrete building column was recovered from the wreckage of the Pentagon. Context:
The Pentagon, completed in 1943 under the urgencies of World War II, was built to provide a central headquarters for an expanded U.S. military. On September 11, hijackers crashed an American Airlines Boeing 757 airliner into the portion of the Pentagon that recently had been reinforced as part of a building renovation and counterterrorism effort. The plane impacted just outside the building and slid nearly halfway through it. It totally destroyed a section of the first two floors of the five-story building. The heavily damaged upper floors initially held but, with an intense fire raging, soon collapsed. Many experts credit the use of coiled reinforcement in the columns (now common practice in earthquake regions) for making the Pentagon as resilient as it was and allowing the upper floors to survive long enough for some of the workers to escape.