A Welsh Triad tells us that the warriors Peredur and Gwrgi – elsewhere given as Arthur’s warriors – were killed fighting Eda Great-Knee at Caer Greu. This defeat was attributed to the desertion of Peredur’s and Gwrgi’s warriors just prior to the battle.
Eda’s character is likely based on an actual eighth-century Northumbrian king.
Source
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century