 During his rule he witnessed a setback in the aspirations of Mercia to dominate its neighbours, following the Battle of the Winwæd and the murder of Penda's son, Peada.He was king during the last decade of the co-existence in England of the Christian Roman rite, centred at Canterbury, and the Celtic rite based in Northumbria.At the Synod of Whitby, in 664, the Roman cause prevailed and the division of ecclesiastical authorities ceased.