The rival dynasty of Northumbrian Kings was represented by Edwin of Deira. Edwin inherited an expanded territory, and added to it with extensive military campaigns that brought him great success. For a time, Northumbria stretched as far south as the river Humber and west as far as Anglesey. Bede records, "Edwin king of the Northumbrians, that is, the people living north of the Humber…was a powerful king and ruled all of the people's of Britain, both Angles and Britons, with the exception of the Kentish folk."
As shrewd politically as he was in battle, Edwin married into the Kentish royal family, solidifying his connections with his southern rivals. Through this marriage, Edwin was courted by the Christians. Edwin was non-committal at first but he did not stop the Pope's emissary Bishop Paulinus from freely preaching within the kingdom. Bishop Paulinus travelled with Edwin's new wife to win Edwin over. In 627 AD, Bede tells us that Ad Gefrin, now called Yeavering, was the site of a mass baptism of Northumbrian converts. Excavation by Dr. Brian Hope Taylor in the 1950's revealed the royal lodgings, including a large timber hall and amphitheatre.
During Edwin's reign the royal court was likely to have been peripatetic, moving between royal centres at York and Bamburgh, and throughout the realm. Finally Edwin's reign was brought to an end with his death in battle in 633 AD fighting the armies of the Mercian king, Penda and the British king Cadwalla at Heathfelth near Doncaster. His son Osfrid also died in battle and his other son, Eadfrith was held captive and later killed. After Edwin was killed the Bishop Paulinus was forced to flee from Northumbria along with the Queen and her daughter Eanfled.
Osric, the son of Edwin's Uncle ruled Deira for a time, and Bernicia passed to Eanfrith, the elder son of Aethelfrith. Both these kings had only a short time in office. Death in battle or assassination left the kingdom in the hands of their enemy, the British king Cadwalla. The two dynasties of Deira and Bernicia were once again sundered and the Northumbrian throne was left open. It was now the turn of the Bernician royal house to wrest power from Cadwalla, and the marauding Penda, who spent a year harrying the people of Northumbria.