The Birth of the Star-Spangled Banner

On the night of September 13, 1814, Francis Scott Key watched the British fleet bombard Fort McHenry in Baltimore Harbor and was so moved by seeing the American flag still flying at dawn that he wrote a poem on the back of a letter in his pocket. That poem, set to the tune of a popular British drinking song, became The Star-Spangled Banner. Key was not a soldier but a lawyer, and he had rowed out to the British fleet to negotiate the release of a captured American doctor. The British allowed him to watch the battle from their ship but wouldn't let him leave until it was over.

Source: Wikipedia