Original: The lyrics come from '' Defence of Fort McHenry '' , a poem written in 1814 by the 35-year-old amateur poet Francis Scott Key after witnessing the bombardment of Fort McHenry by Royal Navy ships in Chesapeake Bay during the Battle of Baltimore in the War of 1812 .
Simplified: Francis Scott Key wrote the words to it in 1814 after seeing British ships attacking Fort McHenry in Baltimore , Maryland during the War of 1812 .