to resolve the differences between the two religions in his kingdom, oswiu called for a in 664. called the synod of whitby it was to decide on when to celebrate easter and what rules the monasteries in northumbria would follow. members of the church were summoned from all over the north. the roman position was given by wilfrid who would afterwards become bishop of northumbria. bishop colmán argued for the ionan calculation of easter given them by columba, founder of their order. oswiu made the decision in favor of the roman practice, uniting northumbria under one religion. it joined northumbrian religious practices to those of the southern english.