Aethelfrith was born in Northumbria in 555, the son of King Aethelric of Bernicia and the grandson of King Ida of Bernicia. He succeeded his uncle Hussa of Bernicia as King of Bernicia in 592, and he became known as the most militarily successful of the early Anglo-Saxon kings. He conquered more territories from the Britons by making them tributaries or driving the Britons clean out of their lands and replacing them wth Angles. In 600, he destroyed the Gododdin army at the Battle of Catraeth, allowing for him to conquer British lands further inland. In 603, at the Battle of Degsastan, his numerically-inferior army destroyed the army of King Aedan mac Gabrain of Dal Riada, causing the Irish kings in Britain to never again wage war against the Anglo-Saxons. In 604, he seized power in Deira, uniting Bernicia and Deira under his personal rule. In 616, he defeated the Welsh of Powys at the Battle of Chester, slaying King Selyf ap Cynan in battle. Aethelfrith then attacked the Christian monastery of Bangor-on-Dee and killed 1,200 monks, with only 50 escaping. That same year, he attempted to have the Deiran claimant Edwin murdered in East Anglia, but King Raedwald of East Anglia decided to protect Edwin. Raedwald attacked before Aethelfrith could assemble a proper army, and Aethelfrith was slain in battle on the east bank of the River Idle.