The Diocese of Limerick was formally established at the Synod of Ráth Breasail in the year 1111. The boundaries of the diocese as arranged at that time have remained practically unchanged to the present day. The diocese includes most of County Limerick, and two parishes in Co. Clare. The patron saint of the diocese is St Munchin; tradition holds that St. Munchin was the first bishop of Limerick and he founded a cathedral which remained the principal church of the diocese until Donal O'Brien, King of Limerick, built St. Mary’s Cathedral in the 12th century.