The Diocese of Limerick was created at the Synod of Rathbreasil in 1111. Its illustrious Bishop, Gilbertus was one of the leading fathers of the reform movement at that time which brought the old monastic system to an end and which replaced it with the diocesan system. The Cathedral of St Mary in Limerick was built later in the twelfth century, and is one of the finest cathedrals in the Church. The Diocese occupies most of County Limerick, and includes the fine mediaeval City Of Limerick on the banks of the Shannon.