Oswiu of Northumbria
The Synod of Whitby in 664 forms a significant watershed in that King Oswiu of Northumbria decided to follow Roman rather than Celtic practices. The Synod of Whitby established the Roman date for Easter and the Roman style of monastic tonsure in Britain. This meeting of the ecclesiastics with Roman customs and local bishops following Celtic ecclesiastical customs was summoned in 664 at Saint Hilda's double monastery of Streonshalh (Streanæshalch), later called Whitby Abbey. It was presided over by King Oswiu, who did not engage in the debate but made the final ruling.