Fell Beasts were creatures that the Nazgûl used to travel after Arwen washed away their horses at the river Bruinen. They were created by Morgoth as an imitation of the Great Eagles. A Nazgûl atop a Fell Beast was flying over the Dead Marshes when Frodo, Sam and Gollum were passing them. The Witch-King and his Fell Beast killed King Théoden at the battle of the Pelennor Fields. The other Ringwraiths rode their Fell Beasts at the Battle of the Black Gate, only to be engaged by the Great Eagles.