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. In 662, Swithelm of Essex was persuaded to adopt Christianity and was baptised at Rendlesham, with Æthelwold present as his sponsor. East Anglia became more closely allied to Northumbria, Kent and lands in the Fens by means of royal marriages such as that between the Northumbrian Hereswitha and the East Anglian Æthilric.