The pre-Reformation Christian church in Ireland was first divided into dioceses at the Synod of Ráth Breasail in 1111, although the dioceses of Dublin and Waterford were founded earlier by Hiberno Norse rulers with bishops consecrated by the Archbishop of Canterbury in England.
4. c. 37) effected the abolition of 10 Church of Ireland dioceses by merger with neighbouring ones.
[1] The Roman Catholic diocesan structure was prohibited under Penal Laws but bishops were consecrated abroad and visited Ireland in secret.
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