The details of the arrival of the Germanic Angles in this area is not to be found in historical sources, According to Bede the founder of the Bernician dynasty was Ida of Bernicia. But he had little detail on the Bernician kings before the reign of Athelfrith of Bernicia ( 616). Bede dated Ida's reign to starting in 547. He also gives the impression that the next four kings had all they could do to hold onto their territory. They had constant battles with the British during this time. Athelfrith was the first to expand the territory at the expense of the British. In 605 Athelfrith united the two kingdoms, Bernicia and Deira, into a single and powerful kingdom called Northumbria.