Closeup of the 15 star flag known as The Star Spangled Banner Flag, that flies over Federal Hill. Skyline of Baltimore. The Star-Spangled Banner Flag or the Great Garrison Flag is the garrison flag that flew over Fort McHenry in Baltimore Harbor during the naval portion of the Battle of Baltimore during the War of 1812. Seeing the flag during the battle inspired Francis Scott Key to write the poem The Star-Spangled Banner, which would later become the national anthem of the United States.