Columbia subject headings:
Franks--History--814-843.
Gregory IV, Pope, -844.
Italy--History--Carolingian rule, 774-887.
Harvard subject headings:
Catholic Church--History.
Church history--Middle Ages, 600-1500
Franks--History--814-843
Gregory IV, Pope, -844.
Italy--History--Carolingian rule, 774-887.
Papacy--History
Popes--Biography
Princeton subject headings: