The Civil War of the Five Kings was a legendary war in Britain as accounted by Geoffrey of Monmouth. It began after the death of Gorboduc when his sons, Ferrex and Porrex, feuded over who would become king of the Britons. Ferrex fled Britain and brought Gauls led by Suhard, king of the Franks, to fight for him. Their army was defeated and Ferrex was killed by Porrex. Porrex reigned as king for a short time until he was killed by his mother, Judon, in his sleep.

Both kings seemed to have died childless and war broke out over who would succeed them. Five different men claimed the kingship of Britain in this war and they continually attacked and massacred each other's men. It is not certain who these five kings were and if they were of the line of Brutus or some were usurpers. Order was not restored until Dunvallo Molmutius came to power. He was the king of Cornwall and was braver and more courageous than all the other kings. He defeated Pinner, the king of Loegria. In response, Rudaucus, king of Kambria, and Staterius, king of Albany, allied together and destroyed much of Dunvallo's land. The two sides met in battle and were stalemated. Dunvallo then took 600 of his men and himself and were clad in the armour of the dead enemies. They led a charge deep into enemy lines where they killed the two kings. After this battle, Dunvallo destroyed the remaining defenses of the kings and pillaged their lands.

The death of the kings ended the civil war and Donvallo established himself as the proper king of Britain. His descendents would rule Britain for many years.