Black serpent
From Tolkien Gateway
File:Anke Eissmann - Falling of the Black Serpent.jpeg
Falling of the Black Serpent by Anke Eissmann.
The Black Serpent was a standard of the Haradrim, and especially the token of a mighty warrior and leader of Men who fought at the Battle of the Pelennor Fields, and was slain by King Théoden of Rohan. It was described as a black serpent upon a field of red.
