The Guelphs and Ghibellines: The History of the Rival Political Factions in Medieval Italy

Papal supremacy in ecclesiastical matters had long been asserted and was, by and large, unchallenged. But in the late 11th century, Pope Gregory VII asserted authority in the temporal sphere as well. In a long dispute with Emperor Henry IV over who had the right to appoint bishops and abbots, Gregory decreed that the pope “alone may use the imperial insignia,” that “all princes shall kiss the feet of the pope alone,” and “that it may be permitted to him to depose emperors.” The popes asser...