Columbia subject headings:
Catholic Church and world politics--Papal documents--Indexes.
Letters, Papal--Indexes.
Papacy--Foreign relations--Sources--Indexes.
Harvard subject headings:
Archivio vaticano--Catalogs.
Catholic Church. Curia Romana--History--16th century--Sources.
Letters, Papal--Manuscripts--Catalogs.
Papacy--History--Manuscripts--Catalogs.
Popes--Correspondence
Princeton subject headings:
Catholic Church--Foreign relations--Sources.
Church and state--Catholic Church--History--Sources.
Papacy--History--Sources--Catalogs.
Popes--Correspondence--Catalogs.