Rivallo (Welsh: Rriallon) was a legendary king of the Britons as accounted by Geoffrey of Monmouth. He was the son of King Cunedagius and was noted as a young king who reigned frugally. Various sources list conflicting dates for his reign: 811–765 BC (see House of Cornwall), 815–797 BC, and 767–743 BC. He is recorded as the misplaced king of Domnonée.
His reign was troubled by disasters. He was noted as being remembered for a rain of blood which lasted three days, a devastating plague, and a great swarm of flies. Despite these problems, he was remembered as king who ruled wisely. He was succeeded by his son, Gurgustius.
(From Wikipedia, the free encyclopedia)