Deira (Old English: Derenrice or Dere) was a kingdom (559-664 AD) in Northern England which probably emerged when Anglian warriors conquered the Derwent Valley in the third quarter of the fifth century. It extended from the Humber to the Tees, and from the sea to the western edge of the Vale of York. It was the southern of the two kingdoms of Deira and Bernicia which later merged to form the kingdom of Northumbria.