Beowulf (partially lost medieval epic poem; 8th-11th century)
First page of Beowulf.
Status: Partially Lost
Beowulf is a very long epic poem and one of the oldest-surviving English-language stories. The manuscript has always been in fragile condition and has proven to be quite the challenge to keep preserved.
In 1731, it became damaged in a fire, and portions of it were too far gone to be accounted for. One large missing excerpt begins and ends in the middle of the climactic fight with the dragon. It is still possible to follow the story even without the missing piece. Other missing portions merely range from missing sentences, various portions of missing letters, and other minor fragments.
Also of note is that it's suspected that Beowulf was passed down orally and written later. Because of this, it is impossible to know if the author included all of the pieces of the story.
The missing portion has never surfaced, even in older translations of the work. Later printings either attempt to recreate the missing sections or include ellipses to indicate the damage. The missing fragment of the story remains as one of the greatest mysteries of English literature.