Columbia subject headings:
Archivio vaticano--Congresses.
Biblioteca apostolica vaticana--Congresses.
Catholic Church--Historiography--Congresses.
Leo XIII, Pope, 1810-1903--Congresses.
Harvard subject headings:
Leo XIII, Pope, 1810-1903--Congresses.
Popes--Historiography--Congresses.
Princeton subject headings: