What was the epic poem about one of knights?

You're likely thinking of Sir Gawain and the Green Knight, a 14th-century Arthurian romance poem written in Middle English. It is considered one of the greatest works of medieval English literature.

Here's why it fits the description:

* Epic Poem: While shorter than some epics, it's a lengthy, narrative poem with an elevated style and themes of chivalry, adventure, and the supernatural.

* One of the Knights: The poem focuses on Sir Gawain, one of King Arthur's most famous knights, and his adventures.

Let me know if you have any other questions!