On the Fourth of July, Americans who celebrate with myriad renditions of “The Star-Spangled Banner” may well know that the lyrics were the handiwork of Francis Scott Key, who composed his immortal poem while watching the Battle of Baltimore. But fewer people are likely to know what led Key – who was a lawyer, not a soldier – to witness the battle in the first place. The answer comes down to the saga of one Maryland doctor. In late August of 1814, the British had marched to the American capital and also invaded Maryland.