Oswiu(both: ŏz`wē), d. 670, king of Northumbria. He succeeded (641) his brother OswaldOswald, Saint,
d. 641, king of Northumbria (633–41), son of Æthelfrith. In exile during the reign of Edwin, Oswald and his brother Oswy became Christians. After Edwin's death Oswald defeated (633) Cadwallon, king of North Wales, and recovered his father's kingdom.
..... Click the link for more information. in Bernicia only, Deira (the other part of Northumbria) having become a dependency of Mercia. However, when he killed PendaPenda,
d. 654, king of Mercia (c.632–654). A noble of the Mercian royal house, he fought (629) the king of Wessex for lands along the Severn River. He then allied himself with Cadwallon of Wales, defeated (632) Edwin of Northumbria, and made himself king of Mercia.
..... Click the link for more information. of Mercia at the battle of Winwæd (654), he not only made himself ruler of all Northumbria but gained actual possession of Mercia and overlordship of the southern English kingdoms. He lost Mercia again to Penda's son Wulfhere in 657. Oswy continued the conversion of England to Celtic Christianity (see Celtic ChurchCeltic Church,
name given to the Christian Church of the British Isles before the mission (597) of St. Augustine of Canterbury from Rome. Founded in the 2d or 3d cent. by missionaries from Rome or Gaul, the church was well established by the 4th cent.
..... Click the link for more information. ), sending missionaries to Mercia and Essex. To resolve the differences between the Celtic and Roman usages of the church in England, the king called the Synod of WhitbyWhitby, Synod of,
called by King Oswy of Northumbria in 663 at Whitby, England. Its purpose was to choose between the usages of the Celtic and Roman churches, primarily in the matter of reckoning the date of Easter (see calendar; Celtic Church).
..... Click the link for more information. (663), at which he gave his decision in favor of the Roman form of Christianity.