Columbia subject headings:
Harvard subject headings:
Gregory I, Pope, approximately 540-604
Nobility--Italy--History--To 1500.
Nobility--Italy--Sicily--History.
Sicily (Italy)--Church history.
Sicily (Italy)--History--To 800
Sicily (Italy)--Social conditions
Princeton subject headings:
Gregory I, Pope, approximately 540-604.
Nobility--Italy--Sicily--History.
Siciliy--History--To 800.