Columbia subject headings:
Pierleoni family.
Popes.
Harvard subject headings:
Anacletus II, Antipope, -1138.
Catholic Church--History--11th century.
Catholic Church--History--12th century.
Gregory VI, Pope, -1048.
Gregory VII, Pope, approximately 1015-1085
Papacy--History--11th century.
Papacy--History--12th century.
Pierleoni family.
Popes
Popes--History--11th century.
Popes--History--12th century.
Princeton subject headings:
Pierleoni family.
Popes.