 In the early 600s Christians in Ireland and Britain became aware of the divergence in dating between them and those in Europe.The first clash came in 602 when a synod of French bishops opposed the practices of the monasteries established by St Columbanus; Columbanus appealed to the pope but received no answer and finally moved from their jurisdiction.It was a primary concern for St Augustine and his mission, although Oswald's flight to Dál Riata and eventual restoration to his throne meant that Celtic practice was introduced to Northumbria until the 664 synod in Whitby.