The calculation of Easter is not easy and the arguments are highly technical, involving astronomy, mathematics and the application of Scripture. No doubt these differences were rehearsed at some length during the Synod but, in the end, the argument for Oswiu came down to one of authority.

Both the Irish and Roman practices were hallowed, in the eyes of their proponents, by their apostolic progenitors. The Irish said that they had their method of calculation from the Apostle John himself, this method having been passed on to the great saints of their own tradition and finally down to Columba, Iona’s founder.