The Synod of Whitby was a seventh century Northumbrian synod where King Oswiu of Northumbria ruled that his kingdom would calculate Easter and observe the monastictonsure according to the customs of Rome, rather than the customs practised by Iona and its satellite institutions. The synod was summoned in 664 at Saint Hilda's doublemonastery of Streonshalh (Streanoeshalch), later called Whitby Abbey

The Synod of Whitby established Roman practice as the norm in Northumbria, and thus "brought the Northumbrian church into the mainstream of Roman culture."[9] The episcopal seat of Northumbria was transferred from Lindisfarne to York. Wilfrid, chief advocate for the Roman position, later became Bishop of Northumbria, while Colmán and the Ionan supporters who did not change their practices withdrew to Iona. Colmán was allowed to take some relics of Aidan, who had been central in establishing Christianity of the Ionan tradition in Northumbria, with him back to Iona. To replace the departing ecclesiastics, Oswiu chose mostly Irishmen who were from the parts of Ireland that kept the Roman Easter (as most of Ireland had done for some time by the 660s).

http://en.wikipedia.org/wiki/Synod_of_Whitby