The Synod of Whitby was a significant church meeting held in 664 AD in Northumbria, England. It aimed to resolve differences between the Celtic Christian practices, represented by Saint Columba and the Roman traditions, represented by Bishop Wilfrid. The main issues included the calculation of Easter and the style of monastic tonsure. At the synod, King Oswiu presided over the discussions, ultimately siding with the Roman practices. This decision led to the adoption of the Roman method for calculating Easter and helped unify the Christian church in England under the authority of the Pope.