Fort McHenrys commanders were almost certain that the British fleet would make their way down the Chesapeake Bay to the Patapsco River to attack the city of Baltimore. Fort McHenry lay at the northwest branch of the Bay leading to Baltimore. Since they knew the battle would take place at the Fort, the commanders wanted a very large flag sewn for the Fort. Major George Armistead said that he wanted the flag to be big enough "that the British will have no difficulty in seeing it from a distance."
So in August of 1813, Mary Pickersgill was contracted to sew "1 American Ensign 30 by 42 feet first quality Bunting $405.90." At that time this would be the largest flag ever flown in the country. It would be over four stories in length.
All during the months of July and August of 1813 Mary and her 12-year-old daughter,
Caroline sewed on they flag. They worked on the floor of a Baltimore brewery.