In 38 BC, the heir to the Parthian throne, Pacorus I was defeated and killed at the Battle of Mount Gindarus by a Roman force. His death spurred a succession crisis in which Orodes II, deeply afflicted by the death of his favourite son, relinquished the throne to his other son Phraates IV. Orodes II died soon afterwards. His cause of death is uncertain. According to Cassius Dio, he had either died of grief due to Pacorus' death, or of old age. Plutarch, however, states that Orodes was murdered by Phraates IV. Fearing that his position might become endangered, Phraates IV executed all his half-brothers–the sons of Orodes and his Commagenian wife Laodice, partially due to their maternal descent being greater than that of his own. Laodice was probably killed as well.