 It served as the pro-cathedral of the Archdiocese of Baltimore until an official cathedral, the Basilica of the National Shrine of the Assumption of the Blessed Virgin Mary, was built in 1821 to alleviate overcrowding at St. Peter's.With an increase of the Catholic population of Baltimore from 800 in 1792 to 10,000, the pro-cathedral was only able to accommodate a tenth of its total parishioners at any given Sunday Mass.The new cathedral was built one block to the north of St. Peter's.