|Why is Saint Mary's Called the PRO-Cathedral?|
"The use of the title Pro-Cathedral was sanctioned by Archbishop Walsh [Archbishop of Dublin from 1885 to 1921] No one, in the seven centuries that have elapsed since the time of Laurence O'Toole, recognized any church in Dublin except that which the saint re-built and enlarged, which he sanctified by his presence and his prayers - Christ Church, the Cathedral of the Holy Trinity. Only the Pope can constitute a church a cathedral. A Pope had constituted one cathedral in Dublin and no successor of St Laurence asked for that decision to be revoked".
- Extract from Dublin's Pro-Cathedral by Mary Purcell (1975)
"Visitors to the church frequently ask why it is called a Pro-Cathedral. It came to be known as such in the 1880s and it was Dr. Walsh who confirmed the use of the title. St. Laurence O'Toole, second Archbishop of Dublin, rebuilt and enlarged Christ Church and it was constituted by the Pope at the time as the Cathedral of the Holy Trinity. In the seven centuries that have elapsed since then no successor of St. Laurence has asked for that decision to be revoked. Until that happens, St. Mary's will continue as the mother church , but without the full title of 'cathedral' of Dublin."
-Extract from Saint Mary's Pro-Cathedral Dublin by Dermod McCarthy, The Irish Heritage Series, Eason and Sons 1988.