1911 Encyclopædia Britannica/Deira
DEIRA, the southern of the two English kingdoms afterwards united as Northumbria. According to Simeon of Durham it extended from the Humber to the Tyne, but the land was waste north of the Tees. York was the capital of its kings. The date of its first settlement is quite unknown, but the first king of whom we have any record is Ella or Ælle, the father of Edwin, who is said to have been reigning about 585. After his death Deira was subject to Æthelfrith, king of Northumbria, until the accession of Edwin, in 616 or 617, who ruled both kingdoms (see Edwin) till 633. Osric the nephew of Edwin ruled Deira (633–634), but his son Oswine was put to death by Oswio in 651. For a few years subsequently Deira was governed by Æthelwald son of Oswald.
See Bede, Historia ecclesiastica, ii. 14, iii. 1, 6, 14 (ed. C. Plummer, Oxford, 1896); Nennius, Historia Brittonum, § 64 (ed. Th. Mommsen, Berlin, 1898); Simeon of Durham, Opera, i. 339 (ed. T. Arnold, London, 1882–1885).