Thus, the metropolitan Diocese of Westminster came to have fifteen suffragan sees, the largest number in the world. Accordingly, by the Apostolic Letter "Si qua est" of 28 October 1911, Pope Pius X erected the new provinces of Birmingham and Liverpool, making these two dioceses metropolitan archdioceses. There remained under Westminster the suffragan sees of Northampton, Nottingham, Portsmouth, and Southwark; to Birmingham were assigned those of Clifton, Newport, Plymouth, Shrewsbury, and Menevia; and to Liverpool, Hexham and Newcastle, Leeds, Middlesbrough, and Salford.