At the Synod of Ráth Breasail in 1111 Ireland was divided up into ecclesiastical dioceses based on territorial units.
Derry was a Columban establishment founded by Columba who was a prince of the Cenel Conaill.
It opposed many of the church reforms as well as being made part of the diocese of the Cenel Eogain.
In 1246 its bishop, Germanus O'Carolan, obtained sanction from Pope Innocent IV to have the see transferred to Derry due to the remoteness of Rathlowry.
By this stage the Columban foundation at Derry had become extinct and was replaced by the Augustinian Order.