Deira
In Roman Britain Deira was separated from Bernicia. The two had a broad area between them where no one lived. The Romans had small defensive works in this area to protect the route to Hadrian's Wall. It was a kind of no man's land after the Angles arrived. Deira first came under the control of the Angles in 560 under their leader Ella. He conquered the Britons in Deira in 581. Deira was still blocked from northward expansion by Bernicia. To the west they were blocked by the last remaining British kingdom of any size, Elmet. King Athelfrith of Bernicia united the kingdoms of Deira and Bernicia into Northumbria. In 617 Edwin of Deira defeated Elmet and expelled their king, Cerdic. Deira and Bernicia were separated again briefly after the death of King Oswald of Bernicia. His brother Oswiu of Northumbria inherited the kingship of Bernicia but did not control Deira until 651. From that time until 867, Deira was treated as a subkingdom of Northumbria. In 867 the Vikings took control of Deira.