Columbia subject headings:
Communication--Religious aspects--Christianity--Congresses.
Gregory I, Pope, approximately 540-604--Congresses.
Sicily (Italy)--Church history--Congresses.
Harvard subject headings:
Gregory I, Pope, approximately 540-604--Congresses.
Sicily (Italy)--Church history--Congresses.
Princeton subject headings:
Communication--Religious aspects--Christianity--Congresses.
Gregory I, Pope, approximately 540-604--Congresses.
Sicily (Italy)--Church history--Congresses.